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I . .JAIL“F.FI2.FF’F,V'.;F,V‘ HFFI'.;$’!'F.u!;F-F:I:I~FF ";'IV!F VFVFI'F ”I FI.I.2$FFIV$FF"F~F W . .5. . III: II" I I. . II“I:" .F’.FF I‘ ‘ Inn." J" Vlly‘l. lI FF H V}. 4““ . ',. :FVVl-FF‘ dd." Vh.FFF*t' fl"? 'IFI‘:FFI,.- ' .I.."I'..I 1 w w: a * r 3 1 {‘5 7.: ‘ Anyjfiu I» ' .J ' P, g.“ i" I P 1:. {if J l Fundam- ~ ”'1" I 1‘,” 3 at A 1.43 a .4, -' 3“ § 1 This is to certify that the dissertation entitled Growth and Photosynthesis of Two Field-Grown Pepulus Clones During The Establishment Year presented by Donald Andrew Michael has been accepted towards fulfillment of the requirements for PhD degree in Forestry Major professor Date 2/24/81: MS U is an Affirmative Action/Equal Opportunity Institution 0-12771 MSU LIBRARIES .—,—. RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. .‘10’ i f) V ‘ - - ' .3.“ . _. ~ \ ;' a; ‘ GROWTH AND PHOTOSYNTHESIS OF TWO FIELD-GROWN POPULUS CLONES DURING THE ESTABLISHMENT YEAR By Donald A. Michael A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Forestry 1984 ABSTRACT GROWTH AND PHOTOSYNTHESIS OF Two FIELD-GROWN PoryLuS CLONES DURING THE ESTABLISHMENT YEAR By Donald A. Michael Photosynthesis and growth' under field conditions were monitored for Egpulus x ggnamgniggga cv. "Eugenei" (Eugenei) and 2. tristis x z. balsamiggna cv. "Tristis #1" (Tristis) during their first growing season. Photosynthetic rates were measured using a portable 1“CD apparatus which allowed intensive sampling within individuaI trees. Diurnal photo- synthesis patterns were determined throughout the growing season for four positions within the crown: (1) an expanding leaf (prior to budset), (2) a recently mature leaf, (3) a leaf in the center of the mature leaf zone, and (4) a lower crown leaf. In addition, photosynthetic rates were deter- . mined for the entire leaf complement of trees selected periodically throughout the growing season. The microenvi- ronment of measured leaves was quantified by measuring photosynthtically-active photon flux density, leaf temper- ature, and relative humidity. In addition, stomatal conduc- tance and C02 compensation points were determined. Weekly morphological measurements of a permanent growth plot and periodic destructive sampling were used to monitor the field Donald A. Michael development of the two clones. Leaf orientation was quantified using a weighted pro- tractor and compass. Vectors normal to the leaf lamina were mathmatically constructed and used to determine the area of each leaf projected toward the sun. The clones exhibited widely different growth patterns. Tristis grew rapidly for #8 days before setting bud in mid- Suly. In contrast, Eugenei grew at a slower rate than Tristis but maintained this rate for 75 days before setting bud in September. Eugenei exceeded Tristis' total leaf area and dry weight by 56 and 37 1, respectively. Eugenei had a higher harvest index than Tristis throughout most of the growing season. The product of stem height and squared stem diameter (measured 2.5 cm above the point where the stem originated on the cutting) was highly correlated with total leaf area in both clones. Photosynthetic rates were low in immature leaves; increased basipetally and peaked in recently-mature leaves; and thereafter declined basipetally in both clones. Diurnal and withinétree photosythesis patterns were highly variable due to differential light interception between leaves. In general, Tristis produced smaller leaves that had higher unit-area photosynthesis rates than Eugenei. Total photo- synthesis integrated over the growing season closely matched dry matter production in both clones. Leaves in Tristis were displayed nearly horizontally, whereas leaves were displayed more vertically in Eugenei. Donald A. Michael Within-tree mutual shading was more pronounced in Tristis; however, light interception in the crown of Eugenei was also reduced since some leaves were situated at oblique angles to the sun. Reductions in light and photosynthesis occured in the, lower-crown in Tristis due to mutual shading whereas light and photosynthesis reductions occurred largely in upper and middle-crown leaves in Eugenei due to the oblique angles formed between the sun and certian leaves within those regions. This work is dedicated to my wife, Jan, in gratitude for her unqualified love and support. ACKNOWLEDGMENTS I wish to express my sincere thanks to Dr. Donald I. Dickmann for his support, guidance and patience during the course of my graduate program. I would also like to give special thanks to Drs. Jud Isebrands and Neil Nelson for their continued encouragement and support. Appreciation is extended to Drs. Flore, Hanover, and Heins for their suggestions, critical review of this manu- script, and for serving on my graduate committee. Grateful aknowledgment is also given to Ms. Judi Henry, Mr. Paul Ehlers, and Ms. Marynell Redman for their friend- ship, valuable technical assistance, and input.into this study, and to scientists at the 0.8. Forest Service's Forestry Sciences Laboratory at Rhinelander, Wisconsin for several informative discussions, and for their professional dedication to forestry research. Finally, gratitude is due to the graduate students and faculty of the Department of Forestry, Michigan State University. TABLE OF CONTENTS Page LIST OF TABLES O O O O O O O O O O O O O O O I 0 Vi LIST OF FIGURES O O O O O O O O O O O O O O O O O Viii INTRODUCTION 0 O O O O I O O O O O O I I O O O O 1 CHAPTER I. Determining Photosynthesis of Tree Leaves in the Field Using a Portable 14C02 Appar- atus: Procedures and Problems . . . . . . . . . 6 Abstract . . . . . . . . . . . . . . . . . . 7 IntrOdUCtion O I O I I O O O O O O O O O O O 8 Methads O O O O O O O O O O O O O O O O O O 9 Results and Discussion . . . . .'. . . . . . 2n Conclusions . . . . . . . . . . . . . . . . 38 References . . . . . . . . . . . . . . . . . #1 CHAPTER II. Growth and Development of Two Field- Grown Panning Clones During the Establishment Year 0 O O O O I O O O O C O I I O O I O O O O O ”5 Abstract 0 O O O O O O O O O O O I O O I O ”6 Introduction . . . . . . . . . . . . . . “7 Methods and Materials . . . . . . . . . . . A7 Resu1t3 O O O O O C I O O O O 0' O O O O O O “9 DiSCUSSion O O O O O O O O O O O O O O O I O 69 References . . . . . . . . . . . . . . . . . 76 CHAPTER III. Characterization of Photosynthesis Within Two Field-Grown Banning Clones During the Establishment Year . . . . . . . . . . . . . . . 80 AbstraCt O O O O O O O O O I O O O O O O O O 81 Introduction . . . . . . . . . . . . . . 82 Methods and Materials . . . . . . . . . . . 83 . Resu1ts O O O O O O O O O O O O O O O 0 O O 91 Discussion . . . . . . . . . . . . . . . . . 124 -References . . . . . . . . . . . . . . . . . 136 CHAPTER IV. Leaf Orientation, Light Interception and Photosynthesis in Two flogging Clones During the Establishment Year . . . . . . . . . . . . . 1““ Abstract 0 O O O O O O O O O O O O I O O O O 1'45 Page Introduction 1"? Material and Methods . . . . . . . . . . . . 148 Results . . . . . . . . . . . . . . . . . . 161 Discussion . . . ,., . . . . . . . . . . . . 173 Appendix A . . . . . . . . . . . . . . . . . 181 Appendix B . . . . . . . . . . . . . . . . . 185 References . . . . . . . . . . . . . . . . . 186 LIST OF TABLES Table Page CHAPTER II 1 Dry weight (g) by date for harvested 1- year-old Tristis and Eugenei trees. One representative tree was harvested per clone on each date shown. . . . . . . . . . . . . . 7O 2 Comparison of developmental parameters of harvested Tristis and Eugenei trees during the first growing season. . . . . . . . . . . 71 CHAPTER III 1 Within-crown comparison of total leaf area, photosynthetically-active photon flux (PPF), whole-leaf photosynthesis (PgL), and light use efficiency (LUE) for Eugenei and Tristis measured 10 July 1979 . . . . . . . . 97 2 Within-crown comparison of total leaf area, photosynthetically-active photon flux (PPF), whole-leaf photosynthesis (PgL), and light use efficiency (LUE) for Eugenei and Tristis measured 8 August 1979. . . . . . . . 99 3 Within-crown comparison of total leaf area, photosynthetically-active photon flux (PPF), whole-leaf photosynthesis (PgL), and light use efficiency (LUE) for Eugenei and Tristis measured 30 August 1979 . . . . . . . 102 -3 -2 A C02 compensation points (cm m ) for varoius leaf positions for Tristis and Eugenei trees by date. Each value repre- sents the average of three determinations . . 103 5 Simple correlation coefficients between photosynthetic rate (PgA), Photosynthetic- ally-active photon flux density (PPFD), leaf temperature (LT), stomatal conductance (CON), and leaf number from the tree base (LNFB) for leaves pooled acropetally in a 1 year-old Tristis tree measured at 10 am (solar time) on 30 August 1979. . . . . . . . 113 Table ’ Page 6 Simple correlation coefficients between photosynthetic rate (PgA), photosynthetic- ally-active photon flux density (PPFD), leaf temperature (LT), stomatal conductance (CON), and leaf number from the tree base (LNFB) for leaves pooled acropetally in a 1 year-old Eugenei tree measured at 10.50 am (solar time) on 30 August 1979. . . . . . . . 114 7 Total diurnal photosynthetic production (mg C02) for single Tristis and Eugenei trees on four days. Whole-leaf photosynthesis rates of each leaf within a tree were inte- grated over a 1” h diurnal period and sum- med to obtain total daily photosynthetic production per tree . . . . . . . . . . . . . 125 8 Comparison of estimated and measured cumu- lative dry weight yield for Tristis and Eugenei trees by date . . . . . . . . . . . . 126 CHAPTER IV 1 Total-tree light interception (PPFt) and photosynthesis (PgT) for Tristis and Eugenei leaves measured between 10.00 and 1u.oo h (solar time) on July 22, 1980 com- pared to estimates for totally unshaded leaves and leaves oriented perpendicular to the sun. . . . . . . . . . . . . . . . . . . . 172 2 Tristis and Eugenei's measured total-tree photosynthesis (PgT) compared to estimates of PgT when leaf orientation (L0), leaf area (LA), or photosynthetic response to light (PPFD/PgA) were held constant between clones. Measured 10.00 to 1A.00 h (solar time). July 22, 1980. Numbers in parenthe- sis indicate percent difference from Eugenei's measured rate. . . . . . . . . . . . 17h LIST OF FIGURES Figure Page CHAPTER I 1A 1 A - complete C02 gas apparatus. 1 - 0.3 1 stainless steel field tank with quick connect coupling; 2 - brass two-stage regu- lator; 3 - flow control valve; A - flow meter; 5 - handpiece; 6 - leather holster. B - Closeup of handpiece. 1 - upper and lower plastic jaws; 2 - recessed gas cham- bers with silicone rubber gaskets; 3 clamping mechanism; 4 - gas inlet to tire valve and transfer chamber; 5 - outlet line; 6 - 002 absorption column; 7 - vent; 8 - alumninum handle 0 o o o o o o o o o o o 10 2 Closeup of handpiece during field use. Note 14C02 gas treatment chamber enclosed by silicone rubber gasket (arrow) . . . . . . 15 3 Within tree sampling scheme for Poppins trees during the first growing season. A - immature leaf, B - recently-mature leaf, C - leaf in center of mature leaf zone, D - lower crown leaf . . . . . . . . . . . . . . 21 A Photosynthetic rates (Pg) of mature £92313; x gunamgnicana cv. 'Eugenei' (circles - 1981 experiment) and E. halsamifena x E. tzistis cv. 'Tristis #1' (stars - 1979 experiment) leaves measured with the 1HC02 and IRGA techniques. The linear equation of best ‘fit for the combined data was: “ACO = 0.16 + 0.68 (IRGA) (1’2 3007) o o o o 25 2 5 Boundary line relationship between gross photosythesis (Pg) and photosynthetically- active photon flux density (PPFD) for recently-mature leaves of field-grown Populgs x gunamgnigana cv. 'Eugenei' trees. The starred data points were used to estab- lish the nonlinear regression line: Pg = 0.85157 - (0.88654 x (0.99689PPFD)). . . . . 29 6 Relationship between gross photosynthesis (Pg) and photosynthetically-active photon flux density (PPFD) for mature flopping x euzamenicana cv. 'Eugenei' leaves using the Figure 1AC02 technique and boundary-line analysis (dashed line and starred data points; Pg = 0.88514 - (0.99372 x (0.99810PPFD))) and the IRGA technique (solid line and open circles; Pg = 0.7904 - (0.83279 x (0.99796PPFD))) . . . . . . . . . . . . . . Gross Photosynthesis (Pg) and photosynthe- tically-active photon flux density (PPFD) profile for a N6-leaf Populus x - gang cv. 'Eugenei' tree measured in the field from 10 to 12 am (solar time), Au ust 30, 1979. LPI = leaf plastochron index LPI 0: the first 30 mm leaf below the apex) . . Boundary-line relationship between gross photosynthesis (Pg) and photosynthetically- active photon flux density (PPFD) for field grown E. x ennamgnicana cv. 'Eugenei' leaves. Only data near the boundary line are shown. (A - expanding leaf, Pg = 0.62766 - (0.73957 x (0.99736PPFD))' B - recently-mature leaf, Pg = 0.85157 - (0.8865H x (0.99698PPFD)); D - lower crown leaf, Pg = 0.7022A - (0.73277 x (0.99653PPFD))) O O I O I I O O O O O O O 0 CHAPTER II Environmental conditions during the 1979 growing season at the Harshaw Experimental Farm near Rhinelander, Wisconsin. Precip. = precipitation (dased lines represent irrigation); ST = soil tension at a depth of 15 cm; Air Temp. = air temperature (squares = maximum, stars = minimum); IFD = irradiant flux density; RH = mean relative humidity. O O O O O I C O O O O O O O O O 0 Changes in height (A), diameter (B) and number of leaves (C) for Tristis (stars) and Eugenei (squares) trees during their first growing season. Twenty-four trees per clone were measured on each date shown. Budset dates are shown with arrows. Dashed lines indicate rates of change. TNL = total number of leaves; D = stem diameter 2.5 cm above the main stem's point of insertion on the cutting; Ht = total tree height. 0 o o o e o o o o o o o o o o o e o Within-tree changes in the number of expanding, mature, and abscised leaves for Page 33 36 39 50 53 Figure Tristis (A) and Eugenei (B) trees during their first growing season. Budset dates are indicated by arrows. TNL = total num- ber of leaves . . . . . . . . . . . . . . . Changes in mean specific leaf weight (SLW) for Tristis (stars) and Eugenei (squares) trees during their first growing season. Budset dates are indicated by arrows. Each point represents the average SLW of all leaves of one tree. . . . . . . . . . . . . Changes in specific leaf weight (SLW) with leaf plastochron number (LPI) for Tristis (stars) and Eugenei (squares) trees for three dates during their first growing season. The location of the first mature leaf below the apex is shown by arrows. LPI O is the first leaf below the apex with a length >»29 mm. . . . . . . . . . . . . . Within-crown leaf area patterns for Tristis (A) and Eugenei (B) trees at four dates during their first growing season. The location of the first mature leaf below the apex is indicated by an arrow. LNFB = leaf number from the tree base; LA = leaf area . Total leaf area (A) and the rate of leaf area development (ASLA) (B) for Tristis (stars) and Eugenei (squares) trees during their first growing season. Budset dates are indicated by arrows . . . . . . . . . . CHAPTER III Expression of photosynthetic rates on a unit area (PgA), unit weight (PgW) and whole-leaf (PgL) basis for Tristis (squares) and Eugenei (stars) leaves mea- sured 30 August 1979. Leaves were pooled for comparison by leaf number from the tree base (LNFB) (A), crown section (B), and leaf plastochron index (LPI) (C). . . . . . Photosynthesis (PgA) by leaf number from the tree base (LNFB) for three measurement dates on which each leaf within each Tristis (squares) and Eugenei (stars) tree was sampled . . . . . . . . . . . . . . . . Boundary line plots of photosynthesis (PgA) versus photosynthetically-active photon Page 56 6O 62 65 67 92 95 Figure flux density (PPFD) (B) and leaf tempera- ture (LT) (A) for Tristis and Eugenei leaves at various positions within the crown. Only data near the boundary lines are shown. Stars (A) = immature leaf; circles (B) = recently-mature leaf; aster- isks (C) = leaf in center of mature leaf zone; triangles (D) = lower-crown mature leafI I I I I I I I I I I I I I I I I I I I Boundary line plots of photosynthesis (PgA) versus stomatal conductance (CON) (0), stomatal conductance versus photosynthetic- ally-active photon flux density (PPFDe) (B), and stomatal conductance versus leaf temperature (LT) (A) for Tristis and ~ Eugenei leaves at various locations within the crown. Only data near the boundary lines are shown. Stars (A) = immature leaf; circles (B) : recently-mature leaf; asterisks (C) = leaf in center of mature leaf zone; triangles (D) = lower-crown mature leaf . . . . . . . . . . . . . . . . The relationship between leaf number from the tree base (LNFB) and photosynthesis (PgA), photosynthetically-active photon flux density (PPFDe), stomatal conductance (CON), and leaf temperature (LT) for each leaf on single Tristis and Eugenei trees measured 30 August 1979 . . . . . . . . . . The relationship between solar time and photosynthesis (PgA), photosynthetically- active photon flux density (PPFDe), stomat- al conductance (CON) and leaf temperature (LT) for Tristis and Eugenei leaves at various crown positions measured during 17 July 1979. Stars (A) = immature leaf; circles (B) = recently-mature leaf; aster- isks (C) = leaf in center of mature leaf zone; triangles (D) = lower-crown ,mature leaf. I I I I I I I I I I I I I I I I I I I The relationship between solar time and photosynthesis (PgA), photosynthetically- active photon flux density (PPFDe), stoma- tal conductance (CON) and leaf temperature (LT) for Tristis and Eugenei leaves at various crown positions measured during 15 August 1979. Stars (A) = immature leaf; Page 105 107 110 115 Figure circles (B) = recently-mature leaf; aster- isks (C) = leaf in center of mature leaf zone; triangles (D) = lower-crown mature leaf. I I I I I I I I I I I I I I I I I I I The relationship between solar time and photosynthesis (PgA), photosynthetically- active photon flux density (PPFDe), stomat- al conductance (CON) and leaf temperature (LT) for Tristis and Eugenei leaves at various crown positions measured during 29 August 1979. Stars (A) = immature leaf; circles (B) = recently-mature leaf; aster- isks (C) = leaf in center-of mature leaf zone; triangles (D) : lower-crown mature leaf. . . . . . . . . . . . . . . . . . . . Total daily carbon uptake for single Tris- tis and Eugenei trees on 15 August 1979. (PgL - whole leaf photosynthesis; LNFB - leaf number from the tree base) . . . . . . CHAPTER IV Leaf axes and vectors used to quantify leaf orientation in Populns leaves. V1 = vector along the leaf midrib (leaf axis #1); V2 = vector perpendicular to V1 in the lamellar plane (leaf axis #2); NL = vector normal (perpendicular) to V and V . . . . . . . . 1 2 The relationship between photosynthesis (PgA) and PPFD for field-grown Tristis and Eugenei leaves during their first growing season. A = upper-crown leaf (LPI 3); B : recently-mature leaf (LPI 9); C = mature leaf midway between B and D; and D = sixth mature leaf from the base of the stem. These curves were generated from data pre- sented in Chapter III . . . . . . . . . . . Leaf azimuth, midrib angle, and lamina angle by LPI for the entire leaf complement of single Tristis and Eugenei trees mea- sured on July 22, 1980. . . . . . . . . . . Equal-area projection of the azimuth and zenith angles of NL for Tristis and Eugenei leaves measured on August 20, 1979. Lati- tude lines denote zenith angle and longi- tude lines denote north azimuth angle . . . Diurnal leaf area projections onto a plane Page 117 119 122 1N9 159 162 165 Figure perpendicular to the sun's rays for Tristis and Eugenei leaves measured on August 20, 1979. I I I It I I I I I I I I I I I I I I I Ratio of total leaf area/total projected leaf area (PROJLA/LA) for Tristis and Eugenei leaves for the diurnal period of August 20, 1979 . . . . . . . . . . . . . . Page 167 169 INTRODUCTION A .predicted shortage of wood fiber due to increased demand (1) and a decreasing land base (10) has prompted interest in improving tree yields. Yields have been vastly increased in agricultural crops by optimizing plant struc- ture and environmental factors which increase a crop's usable components (3). In a similar manner, experimental intensive cultural systems have been used in an attempt to provide optimum conditions for tree growth (2,3,9). Inten- sive culture systems use some combination of genetically- improved planting stock, irrigation, fertilization, weed and pest control, short rotations, and dense spacings to promote rapid stand growth and high yields. Intensive culture short-rotation (SRIC) systems have several advantages over conventional forest management. For example, SRIC provides : 1) rapid and complete utilization of the site, 2) a secure, sustained, and controlled fiber source, 3) a rapid return on investment, A) high yields, and 5) -an opportunity to produce fiber tailored to a specific end-use. Of course, there are also problems associated with SRIC: 1) SRIC plantations can be genetic monocultures which are prone to disease and insect problems, 2) SRIC requires high inputs of energy and capital, and 3) SRIC has a rel- atively low return on investment (u). However, these prob- lems are not insurmountable. Disease and insect problems can be minimized by careful species and clonal selection, by planting mixtures of species and clones, and by matching specific species and clones to individual sites; energy and capital inputs can be minimized by developing more efficient cultural techniques; and the return on investment can be improved by increasing per hectare yield. Yield 134 a critical factor affecting the economic feasibility of SRIC plantations (11). Maximum wood yield can be obtained under SRIC by selecting species which have rapid juvenile stem growth and by optimizing growing condi- tions. Since, on certain sites, Poppins species are the fastest growing trees in the Lake States (U.S.A) and produce fiber which is readily usable in the forest products indus- try (5), poplars have become one of the most promising species for SRIC systems (12). Poplar yields can be system- atically increased only if the physiological components of yield are identified and if knowledge of how these compo- nents are influenced by cultural and environmental variables is obtained. Biomass yield in trees is based on the integrated production and utilization of photosynthate by individual leaves. Factors which influence yield do so by directly or indirectly influencing photosynthate production or part- itioning. Therefore, an examination of the photosynthetic process is required if yield is to be understood. Earlier work (6,7,8) established base-line data which described the processes of leaf initiation and development, and photosyn- thate production and partitioning in young £92213; trees grown under controlled environmental conditions. As a log- ical extension of this work, experiments were conducted to examine the growth, CO fixation, and autecology of two contrasting Egpulgs clone: growing under field conditions. The objectives of this research were to determine how much CO was fixed, where it was fixed, and what were the major fictors influencing C0 fixation. More specifically, the intent was to quantify Siurnal and seasonal changes in single leaf and whole-tree photosynthesis in relation to tree development in the first growing season. Data were also gathered in two- and three-year-old plantations, but these data are not reported in this dissertation. It was hoped that some of the data and techniques developed in the field examination of these two poplar clones would lead to the development of principles that would apply to other clones and species. In addition, it was hoped that field experimentation would provide insight into which factors or groups of factors merit further controlled environment investigation. References 1. Auchter, R.J. (1976) Raw material supply. TAPPI 59:50- 53. Bowersox, T.W. and W.W. Ward (1976) Growth and yield of close-spaced, young hybrid poplar. For. Sci. 22zfl49- 854. Dawson, D.H., J.C. Isebrands and J.C. Gordon (1976) Growth, dry weight yields, and specific gravity of 3- year-old Populus grown under intensive culture. USDA For. Serv. Res. Pap. NC-122. DeBell, D.S. and J.C. Harms (1976) Identification of cost factors associated with intensive culture of short- rotation forest crops. Iowa State J. Res. 50:295-300. Dickmann, D.I. and K.W. Stuart (1983) The culture of poplars in eastern north America. Michigan State University, 168 p. Dickmann, D.I. (1971) Photosynthesis and respiration by developing leaves of cottonwood (£22212: deltcidea Bartr.). Bot. Baz. 132:253-259. Isebrands, J.C., and P.R. Larson (1973) Anatomical changes during leaf ontogeny in Populug geltgiggs. Amer. Larson, P.R., and J.C. Gordon (1969) Leaf development, 10. 11. 12. 1A photosynthesis and C distribution in figpglus deltgifigs seedlings. Amer. J. Bot. 56:1058-1066. McAlpine, R.G., C.L. Brown, A.M. Herrick, and H.E. Ruark (1966) "Silage" sycamore. Forest Farmer 26:6-7. Rose, D.W. (1976) Economic investigations of intensive silvicultural systems. Iowa State J. Res. 50:301-315. Rose, D.W., K. Ferguson, D.C. Lothner, and J. Zavitkovski (1982) An economic and energy analysis of poplar intensive culture in the Lake States. USDA For. Serv. Res. Pap. NC-196. Zavitkovski, J., J.C. Isebrands, and D.H. Dawson (1976) Productivity and utilization potential of short-rotation £92212; in the Lake States. In: Proc. Symp. on eastern cottonwood and related species, pp. 392-fl01. Greenville, Miss., Louisiana State Univ. Div. Cont. Education. CHAPTER I DETERMINING PHOTOSYNTHESIS OF TREE LEAVES IN THE FIELD 19 USING A PORTABLE CO APPARATUS: 2 PROCEDURES AND PROBLEMS Submitted to PHOTOSYNTHETICA Abstract A field approach for studying photosynthesis in Egpglug leaves is described. Photosynthetic rates were measured using a portable 1“CO apparatus. A paired comparison in- dicated that photosynEhetic rates measured with the 1“C0 device exceeded those measured with an infrared gas analyze: by 5 percent. One hundred to 150 single-leaf photosynthesis and companion environmental measurements could be completed within one day, allowing intensive sampling within trees. Measurements from permanent growth plots located within the experimental plantation were used to identify sample trees. In the first growing season, four leaf positions were sam- pled on a diurnal and seasonal basis. Lateral branches and current terminals were sampled in a similar manner in older trees. Boundary line analysis was used to establish photo- synthetic response curves. Field response curves establish- ed with the boundary line technique compared favorably with those established under laboratory conditions for similar leaves. Wen Biomass yield in trees is ultimately determined by the integrated production and utilization of photosynthate by individual leaves. To study the physiological basis of yield, patterns of C0 assimilation and photosynthate dis- tribution must be identified through field experiments which determine the effects of leaf development, leaf position and orientation, leaf aging, and tree development on total photosynthate production. In addition, the sensitivity of leaves to numerous environmental conditions must be assessed on a diurnal and seasonal basis. Tree crowns are very complex, with leaves of several different age classes located on different orders of bran- ches (Isebrands and Nelson 1982). An equally complex sampl- ing scheme is required to obtain data from these different leaf populations, necessitating a measurement system that produces rapid and accurate determinations of photosynthe- sis. Several researchers have experimented with simple, rapid methods of measuring photosynthesis using 1“CO (Austin and Longden 1967, McWilliam gt 31. 1973, Bell an: Incoll 1981). These methods use miniature chambers to ex- 14 pose sections of leaf lamina to a short pulse of a C0 - 12 2 C0 gas mixture. The exposed discs are excised and as- 2 14 sayed for CO activity. In this manner, several leaf 2 positions throughout a tree crown can be quickly measured with a minimum of leaf disturbance. Moreover, the photo- synthetic contribution of individual leaves in different portions of the crown can then be assessed on a diurnal and seasonal basis. Several 1"CO devices do not permit light interception on the abaxial lea? surface during measurement (e.g., Bell and Incoll 1981). However, abaxial light can be important in driving photosynthesis (Moss 1964), especially in plants with upright leaf displays. Therefore, a 1“C0 (apparatus is needed which permits both adaxial and abaxialzlight inter- ception. 14 This paper describes a CO technique modified from those described by Incoll and Wright (1969) and McWilliam gt 31. (1973). The equipment is inexpensive, relatively easy to construct, simple to operate, allows adaxial and abaxial light interception during measurement, and provides accurate field measurements of photosynthesis. In addition, field sampling procedures are discussed and a technique is des- cribed which can be used to analyze field photosynthesis data. “HP The QQZAfimm The CO appartatus consists of two components: (1) the gas systemzand (2) the handpiece (Fig. 1). 14 12 The Gas §ystgm-- The CO - CO gas mixture used in 2 2 this system can be generated as described by Shimshi (1969), McWilliam gt al. (1973), and Neilson (1977) or pre- mixed and analyzed gas can be obtained from commercial producers. The gas used in our field experiments was 10 14 Figure 1. A - complete C0 gas apparatus. 1 - 0.3 1 2 stainless steel field tank with quick connect coupling; 2 - brass two-stage regulator; 3 - flow control valve; 4 - flow meter; 5 - handpiece; 6 - leather holster. B - Closeup of handpiece. 1 - upper and lower plastic jaws; 2 - recessed gas chambers with silicone rubber gaskets; 3 - clamping mechanism; 4 - gas inlet to tire valve and transfer cham- ber; 5 - outlet line; 6 - CO absorption column; 7 - vent; 2 8 - alumninum handle. ll 12 purchased from Matheson Gas Products. Our mixture contained 322 cm3m-3C0 , with a specific activity of 185 KBq l-1 at 21.100 and 7 atmosphere. The gas was stored in a 7 1 aluminum tank purchased from Matheson. A smaller 0.3 1 stainless steel cylinder (Matheson Model 8x) was filled from the storage tank for use in the field. The field tank was sealed by a hand-operated valve and connected to a Swagelok quick-connect coupling by brass and stainless steel fittings (Fig. 1A). Pressure was reduced by a brass 2-stage regula- tor (Matheson Model 3322) which was supplied with an outlet needle valve. Gas flow was further controlled by a high resolution flow control valve (Airco Series 32 HRV). Tygon tubing was used to connect the flow valve to a flow meter (Matheson Series 7360, Model 602) and from the flow meter to the handpiece. The entire gas system and handpiece was supported by a leather holster which can be clipped to a strap or belt. Total weight of the gas system was 3 kg. Ing flgngglggg -- The pistol-shaped handpiece was mod- ified from that described by McWilliam gt gl. (1973) and consisted of two transparent plastic jaws and an aluminum clamping lever and handle (Fig. 18). Each jaw was recessed to accept a silicone rubber gasket. When pressed together, the gaskets formed a miniture leaf chamber with a diameter of 11 mm and a volume of 0.19 cm3. The lower jaw contained a tire valve and gas transfer chamber. The clamping lever closed the plastic jaws, sealed the leaf chamber, triggered the tire valve and released gas from the field tank through 13 the transfer chamber and into the upper and lower leaf chambers. The gas then exited through outlet tubes in the leaf chamber, passed through a sodium hydroxide CO -absorp- tion column in the pistol grip, and vented to tn: atmos- phere. The sodium hydroxide was changed frequently to en- sure adequate absorption of the outgoing 1“CO , especially when the apparatus was used indoors or in poogly ventilated areas. The total weight of the handpiece was 455 g. BMW 1: The field tank was filled to approximately 7 X 10 kg m2 pressure from the large storage tank. This was enough gas to make 100 to 120 measurements. After setting the delivery pressure to 0.5 X 10” kg me, the aluminum handle on the field gas regulator was removed to prevent accidental adjustment. The flow control valve was also protected. In the field, the outlet needle valves were opened fully and the flow control valve adjusted to provide a flow rate of 1.3 X 10.3 l s-1. Flow rates between 1.0 and 2.0 X 10.3 l 3-1 are required to ensure that photosynthesis is not limited by the supply of C0 (Strebeyko 1967, McWilliam gt g;. 1973, Naylor and Teaie 1975). An optimum flow rate should be determined for each species studied from prelim- inary experimentation. The upper and lower rubber chamber gaskets were coated with a thin layer of silicone grease to provide a seal between the leaf and gaskets and to mark the location of the exposed disc. A section of leaf lamina free from large 1n veins was selected midway between the leaf tip and base, and the exposure chamber clamped firmly onto the leaf (Fig. 2). A 20 a pulse of gas, timed with a stopwatch, was then admin- istered simultaneously to both sides of the leaf. During the treatment period, the leaf was held in its natural orientation. At the end of the 20 3 pulse, the chamber was quickly removed and the center of the exposed disc excised using a #4 cork borer (diameter = 7 mm). The leaf disc was then .forced from the cork borer with a glass rod into a scintillation vial containing 1.5 ml NCS tissue solubilizer (Amersham/Searle). The vial was tightly capped and taken to the laboratory for 1uC-analysis. Several companion measurements were taken to quantify _ the leaf's environment and condition during the measurement period. These measurements included: 1. Leaf temperature - Measured on the abaxial leaf surface with a YSI Model 427 stainless steel thermistor. 2. Air temperature - Measured in the shade of the leaf as above. 3. Diffusive resistance - Measured on the abaxial and adaxial leaf surfaces with a LiCor Model LI-65 autoporo- meter. 4. Photosynthetically-active photon flux density (PPFD, 400 to 700 nm) - Measured at leaf level in the adaxial and abaxial leaf planes, horizontally at leaf level, horizontal- ly above the tree, and toward the sun with a LiCor Model LI- 185 quantum sensor and meter. 15 14 Figure 2. Closeup of handpiece during field use. Note CO 2 gas treatment chamber enclosed by silicone rubber gasket. 17 5. Relative humidity - Measured within the tree crown for each sample tree using an American Instrument Company hygro- meter and narrow range hygrosensors. 6. Leaf orientation - Vertical angles of leaf axes parallel and perpendicular to the leaf midvein were measured using a protractor and weighted nylon cord (Max 1975). Leaf direct- ion was determined using a Silva compass. r Finally, sampled leaves in our studies were excised at the base of the petiole, the cut surface placed in a vial of distilled water, and taken to the laboratory for. determina- tion of C0 compensation points (Dickmann and Gjerstad 1973) and measuriment of leaf area (LiCor Model LI 3000 leaf area meter)'and dry weight (oven-dried at 100°C). Aiaax £2: Radioactixitx After returning to the laboratory, 1.5 ml of 0.5% benzyl peroxide in toluene were added to each vial to bleach out color and the leaf discs were digested for 24 h in an oven at 50°C. After the digestion period, three drops of glacial acetic acid and 13 ml of scintillation cocktail containing 63 ml Spectrafluor (Amersham/Searle) in 1 l tol- uene were added to the vials. The vials were placed in a darkened chamber for 3 h to reduce the effects of chemillum- inescence and were then counted with a liquid scintillation spectrometer (Beckman Model LS 150). Eelsulailflz EBQLQAXBIDQLIQ Bel: 14 Photosynthesis was calcualted from the C0 assay 2 from: 18 Pg : (CPM/CE x CCO x 1.18)/(SA x LA x T) (1) 2 where: -2 -1 Pg = gross photosynthesis rate (mg CO m s ) 2 CPM = sample counts per minute (corrected for background radiation) CE = counting efficiency of the liquid scintillation spec- trometer (expressed as a decimal) CCO = concentration of CO at a standard temperature and preisure (determined in ofir case from Matheson's calibra- tion) (mg CO2 1-1) 1.18 = a discrimination factor to account for diffusive and biochemical discrimination against 1“CO (Van Norman and Brown 1952, Austin and Longden 1967) 2 SA = the specific activity of the 1”C0 -12C0 gas mixture at the same standard temperature and preisure is in CCO (dpm 1.1 gas mixture) 2 LA = the area of the excised leaf disc (m2) T = time length of the 1“002 pulse (3) 1 Photosynthetic rate on a dry weight basis (mg C0 g s 1 2 ) was calculated bysubstituting oven-dry weight of the ex- cised leaf disc in g for LA in (1), using specific leaf weight to estimate the weight of the disc. In addition 9 -1 - photosynthesis can be expressed per leaf (mg CO 3 leaf 1 -1 -1 2 ), or per tree (mg C0 3 tree ). 2 14 M008 nefWoost cmwmm £9 2 Wmmmmunms Photosynthesis was measured on identical areas of the 19 same leaf using an infrared gas analyzer (IRGA) and the 14 ' 14 CO device to test the reliability of the C0 method. 2 14 2 The air entry connection of the CO handpiece was linked to an electric switching solenoid (Skinner Electric Valves). The solenoid was used to alternate the entry of outside air (322 cm3 m-B) or radioactive gas (311 cm3 in.3 CO , 194 KBq l.1 at 21.1 0C and 1 atm.) into the photosyntheiic chamber of the handpiece. The exit connection of the 1“C0 hand- piece was linked to a differential IRGA and then t6 a C0 absorbing column. The gas was then vented to the atmosf phere. In 1981, photosynthetic measurements were made on ten mature leaves from three different trees of Eggglgg x gun; gmgglggng cv. 'Eugenei' (NC 5326), grown in pots in the field for four months under natural light conditions. The leaf plastochron index (LPI; Larson and Isebrands 1971) of sampled leaves ranged from 5 to 9 and the plants had 25 to 30 leaves. Multiple samples were taken on some leaves. Measurements of photosynthesis were made in -sequence, first by the IRGA method, followed by the 1”CO method. The handpiece was clamped onto a portion of leaf Iamina located midway between the leaf tip and base. Air from outside the laboratory was then passed through the chamber and into the IRGA at a flow rate of 2.4 X 10 -3 l s-1. The rate of —photosynthesis was determined from the IRGA after equilib- rium had been attained. The solenoid switch was then trig- gered, shutting off the outside air and releasing a 203 20 pulse of 1“CO -labelled air which passed over the same portion of the Ieaf at a flow rate of 1.3 X 10.3 1 3-1. The exposed leaf disc was then quickly excised and processed as described earlier. PPFD varied from 135 to 636 u mole m-2 s.1 during the experiment, but was constant for each sample. A similar comparison was conducted in 1979 in which thirteen leaves (LPI's ranging from 3 to 12) on two green- house-grown 2. tglggmttggg x E. tzittig cv. 'Tristis #1' (NC 5260) trees (with 18 and 23 leaves) were measured. In the 1979 comparison, a 150 mm plexiglass cuvette was used for the IRGA measurement (Nelson and Ehlers 1983) instead of using the handpiece's chamber for both the IRGA and 1“CO 2 measurements. WWW Several leaves were sampled within systematically selected "average" trees. An "average" tree was defined as a tree whose height and number of leaves (or crown size) approximated the plantation mean. Mean values were obtained from weekly measurements of trees in permanent growth plots in our plantation. In one-year-old trees, diurnal photosynthesis measure- ments were conducted on two-hour increments at four physio- logically important leaf positions (Fig. 3), comprising three oblique and one horizontal age series (Dickmann 1971). The first oblique age series, A, was located in the upper portion of the crown and consisted of an expanding or im— mature leaf (i.e., LPI 3 or 4). The second oblique series, 21 Figure 3. Within tree sampling scheme for Egpglng trees during the first growing season. A - immature leaf, B - recently-mature leaf, C - leaf in center of mature leaf zone, D - lower crown leaf. POSITION LEAF p A V V‘.‘ I...» 22 55.... D.I.; by5b I b be.“ P .17 Do I). D’ D P'/ TIME 23 B, was located in the mid-upper crown region and consisted of a recently-mature leaf. The third oblique series, C, was located in the mid-lower crown region and consisted of a leaf which had reached maturity several days prior to mea- surement. The horizontal age series, D, was located in the lower-most crown region and consisted of a leaf which reach- ed maturity early in the growing season. A Daily leaf length measurements were taken on all leaves on sample trees begin- ning three days prior to the Pg measurement to ensure that this sampling scheme was maintained throughout the growing season. Within-tree photosynthetic patterns were determined by measuring Pg of each leaf on selected trees at 10 to 12 am (solar time) on days spaced equally throughout the grow- ing season. In two-year-old trees, diurnal measurements were taken at four leaf positions (A,B,C,D; Fig. 3) on the current terminal and on first-order lateral branches in the upper, middle and lower crown regions. Odd-numbered leaves (i.e. LPI 1,3,5, etc.) were measured on these shoots from 10 to 13 am (solar time) throughout the growing season to examine developmental Pg patterns. Three-year-old trees were samp- led in a similar manner, although the inclusion of second- order lateral branches increased the complexity by an addit- ional order of magnitude. Boundary ttgg Analysis 9; Etglg Photosynthesis Qgtg Boundary line analysis (Webb 1972, Hinckley gt g1. 1978) was used to interpret the field photosynthesis data. 24 The validity of the boundary-line technique was tested on seven figpglylg x ggzgmgniggng cv. 'Eugenei' trees with 23 to 28 leaves grown in pots in the field. The boundary line for Pg and PPFD in the field was established by measuring 23 mature leaves (LPI 15 or 16) with the 1“C0 device. A Pg/PPFD saturation curve was also eatablished In the labora- tory using an open IRGA system (Nelson and Ehlers 1983) and one mature leaf (LPI 15) from two 'Eugenei' trees selected from the same population of potted field plants. Least- square curves were then fit to the data by computer using the Gaussian method of successive approximations to an asym- ptotic model: PPFD Pg=a-bD -2 -1 where: Pg = gross photosynthetic rate (mg CO m s ) 2 a,b,D = regression parameters -2 -1 PPFD = photon flux density (umoles m s ) Mariam 1a In general, photosynthetic rates measured by the C0 2 technique exceeded those measured by the IRGA by 5 percent (Fig.4). A paired t-test indicated, however, that there was not a significant statistical difference between the two methods (P = 0.05). A slight difference between the two methods was expected since it is generally assumed that a 14 short exposure of CO results in an approximation of gross 2 photosynthesis rather than net photosynthesis, as measured 25 Figure 4. Photosynthetic rates (Pg) of mature £92313; x gugamecicang cv. 'Eugenei' (circles - 1981 experiment) and 2. tglggmlfiggg x E. tzigtig cv. 'Tristis #1' (stars - 1979 14 experiment) leaves measured with the CO and IRGA tech- 2 niques. The linear equation of best fit for the combined 14 2 data was: CO = 0.16 + 0.68 (IRGA) (r =0.7). 2 CO2 UPTAKE (”002), mgCOzm'zs‘1 1.2 0.8 0.4 26 0 0 0 0 0 000 .0 0 0 0 0 0 a. 0 on “.I I 0 We e . I 0 f ‘F r r l 0.4 0.8 1.2 CO2 UPTAKE (IRGA), mgCOZm’zs’1 27 by the IRGA (Turner and Incoll 1971, McWilliam gt g1. 1973, Naylor and Teare 1975, Zelawski and Walker 1976, Incoll 1977). However, an underestimate of gross photosynthesis is more likely since there are possible sources of error asso- ciated with the use of isotopic methods due to physical and 14 biochemical discrimination against CO at the diffusion 2 . sites and perhaps at the carboxylation sites within the lea mesophyll (Van Norman and Brownu1952, Yemm and Bidwell 1969, 12 Incoll 1977): dilution of C0 within the leaf by CO 2 2 evolved from the respiratory pathways (Vozensenskii gt g1. 14 1971, Incoll 1977); and evolution of CO from photorespir- ation (Roberts and Keys 1978, D'Aoust and2Canvin 1972). The extent of these errors is not known; however, the 14C0 device described here provides estimates of photosynthesii for 332312; leaves which closely compare to those determined using the IRGA method. Photosynthesis rates measured with the 1«C0 device probably lie somewhere between gross and net photoiynthesis. A major task in field photosynthesis research is designing a sampling strategy. In most cases, environmental conditions cannot be controlled in the field, but rather, only monitored. When leaves are studied in their natural orientation, dramatic differences in microenvironment occur, even between adjacent leaves of the same tree. In addition, continuous changes are induced by cloud movements and the sun's diurnal and seasonal movements. As a result, true replications of any measurement are difficult, if not impos- 28 sible, to obtain in the field. Lack of replication may trouble workers who are accustomed to controlled-environment laboratory research; however, as Helms (1976) suggested, problems in the field may be resolved with a lesser degree of precision, but a high degree of ecological relevance is usually attained. The first step in designing a sampling strategy is to develop criteria for selecting sample trees. A limited number of leaves can be sampled in the field during a day. This sample can consist of a few leaves from several random- ‘ ly selected trees or several leaves from a few trees select- ed systematically. Given the difficulties in obtaining true replication in the field, we found that it was more inform- ative to sample several leaves on a few systematically selected "average" trees. Sampled leaves must represent physiologically impor- tant populations within the crown. The leaf sampling scheme used here comprised three oblique and one horizontal age series (Dickmann 1971). The oblique age series yielded information on the effects of time of season, stage of plant development, and leaf position on diurnal .photosynthetic capacity. The horizontal series yielded information on the effect of leaf aging at the same leaf position on diurnal photosynthetic capacity. By using this sampling scheme, the photosynthetic activity of leaves of various ages and posit- ions was monitored on a diurnal and seasonal basis and under a wide range of climatic conditions. This information 29 Figure 5. Boundary line relationship between gross photosynthesis (Pg) and photosynthetically-active photon flux density (PPFD) for recently-mature leaves of field- grown £92213; x ggngmgniggng cv. lEugenei' trees._ The starred data points were used to establish the nonlinear PPFD regression line: Pg = 0.85157 - (0.88654 x (0.99689 )). .30 p1 N1 m R L E 283. .Eaa .opor 31 provided a dymanic view of the photosynthetic development of average Eggglgg trees. When data obtained from field measurements of Pg are plotted against a single environmental parameter such as PPFD, a scatter of points always results (Fig. 5). The scatter occurs because uncontrolled variables influence the relationship between the two plotted variables. Boundary line analysis is a technique, proposed by Webb (1972) and used extensively by others (e.g., Hinckley gt g1. 1978) where all values for two variables are plotted and a line enclosing these points is established. This line represents the limiting effect of the independent variable on the dependent variable; it is assumed that values below this line result from the influence of another independent vari- able or a combination of limiting variables (Webb 1972, Hinckley ii 31. 1978). .Boundary line analysis is a useful tool for analyzing data from studies where interacting variables cannot be con- trolled or, in many cases, even identified (Hinckley gt g1. 1978). However, definition of the exact shape and limits of the boundary line is difficult and often very subjective. When possible, the shape of the boundary line should be established from controlled environmental studies that are either done by the researcher or obtained from the liter- ature. If the boundary line is drawn to enclose all points, no allowance is made for sampling error, i.e. the deviation 32 above and below the "true" boundary line. Instead, a body of exterior points must be identified through which a regression line can be derived using standard statistical techniques. An exterior body of points can usually be identifed for relationships which are either linear or asym- ptotic. For example, if a relationship is asymptotic with a positive slope, an increase in the independent variable (x) corresponds to an increase or stabilization of the dependent variable (y). Thus, after an increase in x, any x-y pair which shows a decrease in y below any previous y value can be excluded from the exterior zone of points. Exterior points are thereby selected along the increasing x-axis whose y coordinate is greater than or equal to the y coordi- nate of any previous point. The star-shaped symbols in Figure 5 were chosen in this way and were used to establish the non-linear regression line representing optimal leaf Pg response to adaxial PPFD. Deriving a body of exterior points by this analytical process will minimize the contri- bution of error to the effect being studied but will not provide a true estimate of error in the statistical sense (Webb 1972). Despite this limitation, the method will alleviate the need to hand-fit boundary line curves and will assist in mathematically describing observed relationships. There was good agreement between the shape of the IRGA light saturation curve and the 1“C02 boundary line curve (Fig. 6). However, the boundary line technique must be used with caution in situations where two or more independent 33 Figure 6. Relationship between gross photosynthesis (Pg) and photosynthetically-active photon flux density (PPFD) for mature Pglegg x ggzgmgnlggng cv. 'Eugenei' leaves using the 14 C0 technique and boundary-line analysis (dashed line and 2 starred data points; Pg = 0.88514 - (0.99372 x PPFD (0.99810 ))) and the IRGA technique (solid line and open PPFD circles; Pg = 0.7904 - (0.83279 x (0.99796 ))). .311 E 208.: .Eaa 8.2 0 1m nl ooom. . F b L r b B lP <0w= IIP , ~00: llllpqullllp lllllllll r 35 variables are highly correlated. For example, a stomatal conductance/temperature boundary line plot may indicate that temperature directly influences conductance, when in fact vapor pressure deficit, which is strongly influenced by temperature, may actually exert the direct effect. The general shape of the Pg curve determined for a single field-grown ngulgg tree agrees with those publiShed for ‘laboratory-grown Populug trees by Larson and Gordon (1969) and Dickmann (1971) (Fig. 7). Variations in Pg between adjacent leaves and among other leaves within the crown reflect the effect of leaf aging and differential light interception. The sensitivity of the 1“C0 technique is demonstrated by its ability to detect within-Eree varia- tions in leaf Pg. Information of this type is important for physiological studies of tree crowns. In addition to entire-tree Pg profiles, diurnal Pg patterns have also been identified using the 1“C0 tech- nique. Since the method samples a portion of tie leaf deStructively, preliminary experiments are necessary to determine whether a single leaf can be measured several times without introducing confounding factors, or whether different leaves must be sampled to establish a diurnal pattern. We have found that a single mature leaf can be used for at least two Pg determinations, one or more on each side of the midrib. If successive sampling of the same leaf would impair the leaf's structural integrity, then adjacent leaves should be sampled. 36 Figure 7. Gross Photosynthesis (Pg) and photosynthetically- active photon flux density (PPFD) profile for a 46-leaf Populus x ggggmggiggng cv. 'Eugenei' tree measured in the field from 10 to 12 am (solar time), August 30, 1979. LPI = leaf plastochron index (LPI 0: the first 30 mm leaf below the apex). 37 30 LPI 20 10 ooom com? 000? com m E 29:: .omnE Fl NI 38 Light saturation curves were developed for Eugenei leaves at three of the four positions described earlier using the boundary line technique (Fig. 8). Leaves at all crown positions reached light saturation at approximately 1100 umole m-Zs-1, or about 50$ full sunlight. However, Pmax varied markedly within the tree. Mature upper-crown leaves (B) attained Pmax rates above 0.83 mg C0 m-Zs-1. The (older' lower- crown and the immature upper-croSn leaves (A and D) had Pmax rates below 0.69 mg C0 m s . - 2 missions“ The CO technique described in this paper gives rapid, accuraEe estimates of photosynthesis for ngglng leaves. The device is inexpensive, portable and facilitates extensive sampling of tree crowns. Field data obtained from this device can be analyzed using the boundary line tech- nique. Sampling schemes must be designed to detect important physiological changes which occur during leaf and crown development. Field conditions impose severe sampling con- straints since rapidly changing conditions make replications difficult, or nearly impossible, to obtain. 39 Figure 8. Boundary-line relationship between gross photosyn- thesis (Pg) and photosynthetically-active photon flux den- sity (PPFD) for field grown E. x gnngmgniggng cv. 'Eugenei' leaves. (A - expanding leaf, Pg = 0.62766 - (0.73957 PPFD (0.99736 )); B Epggcently-mature leaf, Pg = 0.85157 (0.88654 x (0.99698 )); D 4 lower crown leaf, Pg PPFD 0.70224 - (0.73277 x (0.99653 ))). X PgA (mg C0, rim-23'”) PgA (mg CO, 17148—1) .40 TRISTIS B 1.2 0.8 0.4 C9.U 800 1é00 2200 1.2 0.8 C9.0 0.4 800 18004 ‘12100 PPFD (,umole m s 1:1 REFERENCES Austin,R.B.,Longden, P.C.: A rapid method for the.measure- ment of rates of photosynthesis using 1“CO .-Ann. Bot. 31:245-253. 1967. 2 Bell, C.J., Incoll, L.D.: A handpiece for the simultaneous measurement of photosynthetic rate and leaf diffusive conductance. I. Design.-J. Exp. Bot. 32:1125-1134, 1981. D'Aoust, A.L., Canvin, D.T.: The specific activity of 14C0 2 evolved in C0 -free air in the light and darkness by 2 sunflower leaves following periods of photosynthesis in 14 C0 . - Photosynthetica 6:150-157. 1972. 2 Dickmann, D.I.: Photosynthesis and respiration by developing leaves of cottonwood (£22213: dgltgidgg Bartr.).-Bot. Gaz. 132:253-259, 1971. Dickmann, D.I., Gjerstad, D.H.: Application to woody plants of a rapid method for determining leaf CO compensation concentrations.-Can. J. For. Res. 3:237-232, 1973. Helms, J.A.: Factors influencing net photosynthesis in trees: an ecological viewpoint. -In: Cannell, M.G.R., Last, F.T.(eds.): Tree physiology and yield improve- ment. Pp. 55- 78. Academic Press, London, 1976. Hinckley, T.M., Aslin, R.G., Aubuchon, R.R., Metcalf, C.L., Roberts, J.E.: Leaf conductance and photosynthesis in four species of the oak-hickory forest type.- For. Sci. 24:73-84, 1978. Incoll, LED.: Field studies of photosynthesis: monitoring with CO .-In: Landsberg, J.J., Cutting, C.V. (eds.): 2 :42 Environmental effects on crop physiology. Pp. 137-155. Academic Press, London, 1977. Incoll, L.D., Wright, W.H.: A field technique for measuring photosynthesis using 14-carbon dioxide.- Spec. Soils Bull., Conn. Agr. Exp. Stn. No. 30, 1969. Isebrands, J.G., Nelson, N.D. Crown architecture of short rotation intensively cultured Eggnlng. II. Branch mor- phology and distribution of leaves and specific leaf weight within the crown of figpglgg 'Tristis' as related to biomass production. - Can. J. For. Res. 12:853-864, 1982. Larson, P.R., Gordon, J.C.: Leaf development, photosynthe- 14 sis, and CO distribution in Egpglgg ggltglggg seed- 2 lings.-Amer. J. Bot. 56:1058-1066, 1969. Larson, P.R., Isebrands, J.C.: The plastochon index as applied to developmental studies of cottonwood.- Can. J. For. Res. 1:1-11, 1971. Max, T.: Crown geometry, light interception and photosyn- thesis of selected Egggltg x ggzgmgzlggng clones. Ph.D. Thesis, Iowa State Univ., Ames, Iowa, 1975. McWilliam, J.R., Phillips, P.J., Parkes, R.R.: Measurement of photosynthetic rate using labelled carbon dioxide. CSIRO Aust., Div. Pl. Ind., Tech. Pap. No. 31, 1973. Moss, D.N.: Optimum lighting of leaves.-Crop Sci. 4:131- 136, 1964. Naylor, D.G., Teare, 1.0.: An improved,1£apid, field method to measure photosynthesis with CO .-Agron. J. 2 43 67:404-406, 1975. Neilson, R.E.: A technique for measuring photosynthesis in conifers by 1“00 uptake. -Photosynthetica 11:241-250, 1977. 2 Nelson, N.D., Ehlers, P.: Comparartive carbon dioxide ex- change for two poplar clones in growthroom, greenhouse, and field. (In Press ) - Physiol. Plant., 1983. Roberts, G.R., Keys, A.J.: The mechanism of photosynthesis in the tea plant (nggllig gingngig L.). - J. Exp. Bot. 29:1403-1407, 1978. Shimshi, D.: A rapid method for measuring photosynthesis with labelled carbon dioxide. -J. Exp. Bot. 20:381-340, 1969. Strebeyko, P.: A rapid method for measuring photosynthetic rate using 1“C0 .-Photosynthetica 1:45-49, 1967. Turner, N.C., IcoIl, L.D.: The vertical distribution of photosynthesis in crops of tobacco and sorghum.-J. Appl. Ecol. 8:581-591, 1971. Van Norman, R.W., Brown, A.M.: The relative rates of photosynthetic assimilation of isotopic forms of carbon dioxide. - Plant. Physiol. 27:691-709,1952. Voznesenskii, V.L., Zalenski, O.L., Austin, R.B.: Methods of measuring rates of photosynthesis using carbon-14 dio- xide. - In: Sestak, 2., Catsky, J., Jarvis, P.G. (eds.): Plant photosynthetic production, manual of methods. Pp. 276-291. Dr. N. Junk, N.V., The Hague, 1971. Webb, R.A.: Use of the boundary line in the analysis of 44 biological data.-J. Hort. Sci. 47:309-319, 1972. Yemm, E.W., Bidwell, R.G.S.: Carbon dioxide exchanges in leaves. I. Discrimination .between 1“C0 and 12C0 in photosynthesis. Plant Physiol. 44:1328-1334, 1969.2 Zelawski, W., Walker, R.B.: Photosynthesis, respiration and dry matter production. In: Miksche, J. P. (ed.): Modern methods of forest genetics. Pp. 89-119. Springer- Verlag, N.Y., 1976. CHAPTER II GROWTH AND DEVELOPMENT OF TWO FIELD-GROWN ZQEHLHS CLONES DURING THE ESTABLISHMENT YEAR Prepared for Submission to PHOTOSYNTHESIS RESEARCH 45 us Abstract. Weekly morphological measurements of trees within permanent growth plots and periodic destructive sampling were used to monitor the field development of two Egpnlgg clones during their first growing season. Tristis (E. . tristis x g. balsamifera) grew rapidly for 48 days before setting bud in July. In contrast, Eugenei (P. x euramericana) grew at a slower rate than Tristis but main- tained this rate for 75 days before setting bud in Septem- ber. The total leaf area and dry weight of Eugenei exceeded that of Tristis by 56 and 37 percent, respectively. In addition, Eugenei had a larger harvest index than Tristis throughout most of the growing season because a greater proportion of photosynthate produce was directed to shoot growth in Eugenei than Tristis; however, a high shoot-root ratio in Eugenei predisposed it to water stress. Differences in above-ground biomass between clones were largely attri- butable to clonal differences in seasonal leaf area develop- ment. 117 Introduction Tree biomass yield is ultimately dependent upon photo- synthate production, redistribution, and utilization. Among other factors, a tree's photosythetic output is related to the size, arrangement, duration, and photosynthetic capacity of its leaf component (21). Photosynthate is then redistri- buted within the plant in response to the demands of various sinks, which in turn respond to several external and intern- al factors (3). Knowledge of such a complex system is best obtained from experiments which quantify patterns of growth, photosynthesis, and photosynthate distribution in the same or similar plants (4,13). We have used this integrated physiological approach in our field studies of hybrid pop- lar. This paper summarizes growth data collected as part of . a large-scale field examination of the photosynthetic properties of two poplar clones during their first growing season. It is important to identify how a tree develops and functions during the establishment year, since growth during this period can greatly influence performance in later years. In addition, knowledge of seasonal changes in leaf and tree characteristics aids in assessing measured patterns of photosynthesis and photosynthate distribution, which will be discussed in later papers. Methods and materials Eléflé fléisfiifll and Cultural Usihflfli Two hybrid poplar clones, £gpglgg x ggngmgziggng cv."Eugenei" (NC 5326) and fl. tztgtig x 2. tglggmlfgng cv. 48 "Tristis #1" (NC 5260) were grown under a short-rotation, intensive culture (SRIC) system (8). The clones (hereafter, Eugenei and Tristis) were established on May 22, 1979 at the U.S. Forest Services' Harshaw Experimental Farm near Rhine- lander, Wisconsin, U.S.A. (450 N 890 W) using 1,040 25 cm unrooted hardwood cuttings per clone planted in blocks at a 0.6 m x 0.6 m spacing. The cuttings were inserted into the soil so that one to two buds were exposed above the soil level. Some trees were later pruned to provide a single main stem. Nitrogen fertilizer (total = 187 kg N ha.1 as NH N0 ) was applied through a gun irrigation system. Soil moistgre status was monitored at a depth of 15 cm using soil tensiometers (Soil Moisture Equipment Corp. Model 2725) and the plantation was irrigated with the gun system when the soil tension dropped below -0.5 bar. Herbicides (triflura- lin and glyphosate) plus additional hand weeding were used to control weed growth. Survival after 20 weeks was 96 and 94 percent for Tristis and Eugenei, respectively. WW Permanent plots located within each clonal block in the main plantation were used to monitor growth. Six 4-tree plots per clone spaced evenly over the plantation were measured weekly to obtain estimates of tree height, total number of leaves, and Stem diameter. Height was measured with a meter stick from the soil surface to the main stem's apex; total number of leaves was determined by counting the leaves present on the main stem in addition to the scars of 49 abscised leaves; and stem diameter was measured with cal- ipers at a permanently marked location 2.5 cm above the main stem's point of insertion on the cutting. These measure- ments were used to periodically select representative trees from the interior of the plantation on which leaf length, leaf area, and leaf dry weight were measured for all leaves. Periodically, representative trees (one tree per clone per date) were harvested and the dry weight of their components (i.e., leaves, stem, cutting, roots) determined. A repre- sentative tree was defined as a tree whose height and total number of leaves approximated the permanant plot mean. Also, the heights, diameters, and leaf numbers of all trees sampled throughout the growing season in the photosynthesis portion of the study were measured in addition to the length, area, and weight of each leaf sampled. WW Hourly measurements of soil temperature, incident ir- radiance, precipitation, and air temperature were obtained from a weather station located 280 m from the plantation. Results MW Daily totals of irradiance, irrigation, precipitation, soil tension, and maximum and minimum air temperatures for the 1979 growing season are shown in Figure 1. Three per- iods of moderately high soil tension (30 June, 13 July, 50 Figure 1. Environmental conditions during the 1979 growing season at the Harshaw Experimental Farm near Rhinelander, Wisconsin. Precip. = precipitation (dased lines represent irrigation); ST = soil tension at a depth of 15 cm; Air Temp. = air temperature (squares : maximum, stars = min- imum); IFD = irradiant flux density; RH = mean relative humidity. ST, —cb AIR TEMP,°C IFD, ly (1‘1 RH, 70 PRECIP., cm ti 51 400 L4; L_L A A A 0 10 20 30 1 l l A L J 0 .0. er. ”4 Nd 0" 140 150 160 170 180 190 200 210 220 230 240 250 260 JULIRN DHYS 10 20 30 10 2C) 30 10 20 30 JUN JUL AUG DATE 10 20 SEP 20 .30 MAY 52 and 14 August) were alleviated by rain or irrigation. Mean daytime air temperatures ranged between 11 and 21 00; how- ever, night temperatures below 4 0C were recorded on three occasions (5 June, 15 August, and 15 September). Irradiance peaked in mid-June and thereafter declined. mmwmmmm Both clones first produced leaves around 29 May. Tristis grew rapidly for 48 days after initial leaf flush and reached its maximum growth rate by 17 July (Fig. 2). Height growth during this period peaked at 2.5 cm d.-1 (Fig. 2a) and leaf production reached a maximum rate of 0.8 leaves a'1 (Fig. 2e). Tristis diameter growth reached a maximum rate of 0.24 mm d"1 sixteen days after height growth and leaf production rates peaked (Fig. 28). The development of Tristis declined rapidly after 16 July as budset approached; however, it continued to surpass Eugenei in height, total number of leaves, and stem diameter until mid-August. Visible term- inal bud formation began in Tristis trees on 23 July, 55 days after intial leaf flush. Ninety-four percent of the Tristis trees in the permanant plots set bud and ceased height and diameter growth by 13 August. The remaining 6% continued to grow until 21 August. Temporal variation in terminal bud formation resulted in dramatic height differen- ces between trees in the planatation and strongly influenced the growth rates presented in Figure 2. Eugenei grew at a slower rate than Tristis during the Figure 2. Changes in height (A), diameter (B) and number of leaves (C) for Tristis (stars) and Eugenei (squares) trees during their first growing season. Twenty-four trees per clone were measured on each date shown. Budset dates are shown with arrows. Dashed lines indicate rates of change. TNL : total number of leaves; D = stem diameter 2.5 cm above the main stem's point of insertion on the cutting; Ht = total tree height. Ht, cm TNL m .2 .3 .4 .5 AD, mm d"1 .1 0 8- -N O.‘ flbl o ro‘ o; ”— (\l -.. ’ o- T O I I r I I I I I [\JLO 17C) 190 210 230 250 270 JULIAN DAYS 20 3010 20 3010 20 3010 20 30 JUN JUL AUG SEP DATE AHt, cm d”1 ATN L, L D—1 > (D O 55 first 59 days after leaf flush (Fig. 2); however, Eugenei produced new leaves and height and diameter increment at this slower rate for 27 days after growth declined in Tristis. During this period, height growth reached a max- imum rate of 1.8 cm d-1 (Fig. 2A) and leaf production reach- 'ed a maximum rate of 0.6 leaves (1..1 (Fig. 20). Eugenei. produced leaves for 23 days after budset occured in Tristis. Height growth and leaf production gradually declined with the onset of terminal bud formation; however, the rate of diameter growth continued to increase and reached a maximum (0.17 mm d-1; Fig. 23) prior to budset. Measurable diameter growth ceased after budset in both clones. The timing of budset in Eugenei was more regular than in Tristis. Approximately 401 of the Eugenei trees in the permanant plots began to form terminal buds on 13 September and all trees attained budset by 24 September. Ellhinzlzsa Leaf ngncaitinn Varying proportions of mature (i.e., not expanding) and immature (i.e., expanding) leaves occurred within the crowns of both clones throughout the growing season. The number of leaves and proportions of leaf types differed between clones as a result of the different growth patterns described above; however, the general developmental pattern was simi- lar between clones. . Early in the growing season over 50% of the leaves present in both clones were immature (Fig. 3A,B). The immature leaf zone increased in absolute size (but decreased 56 Figure 3. Within-tree changes in the number of expanding, mature, and abscised leaves for Tristis (A) and Eugenei (B) trees during their first growing season. Budset dates are indicated by arrows. TNL : total number of leaves. TNL TNL 57 [:1 TOTAL 0 MATURE o EXPANDING 8‘ TRISTIS A ABSCISED 0.. V' .. - 2 E‘:”J 84 :3 .. 5 A O. N a 0‘ u O‘LEH r I * "’A~~~~ ‘. 8‘ EUGENEI e, g. B O N. 04 "M‘F r __#*’I’~’ I r Ciao 200 220 240 A MJUAN DAYS 30 10 20 30 10 20 30 10 JUN JUL AUG SEP DATE 58 as a proportion of total leaf number) as the number of leaves increased. The immature leaf zone in Tristis de- creased rapidly in size after 17 July (Fig. 3A), probably due to a slower rate of leaf production at the apex in conjunction with a constant rate of acropetal leaf matura- tion. This decrease directly preceded terminal bud form- ation. The last 2 to 3 leaves produced by the apex contin- ued to expand slightly for 1 to 2 days after the terminal' bud began to form; however, they failed to attain normal mature leaf size and in most trees, these latter-formed leaves quickly abscised. After budset, leaf production and leaf expansion ceased; as a consequence, Tristis had mature leaves ranging in age from 1 to 70 days. Its mean foliage age increased thereafter. The developmental pattern in Eugenei was similar to that observed in Tristis, however, the entire sequence was extended over a longer period of time and involved more leaves (Fig. 38). The immature leaf zone in Eugenei in- creased in size to approximately 10 leaves; the size of the immature leaf zone slowly decreased after 10 August as the rate of leaf intiation declined prior to budset; and, after budset, all leaves were mature. Leaf abscission began in mature lower-crown leaves and proceeded acropetally in both clones. Abscission began during mid-July and mid-August for Eugenei and Tristis, respectively. Eugenei lost a greater number of leaves in the lower crown than Tristis; however, as of 10 September, 59 both clones had lost approximately 101 of TNL. Mangggning leaf spot and Melampsoza rust were associated with deterior- ating leaves of both clones. §2££1Ii£ Leaf Nsisnt Dexelgnmenl Specific leaf weight (SLW, leaf dry weight/leaf area) varied between. clones and within individual trees. In addition, within-crown SLW patterns changed over the growing season. Average SLW per tree (SEW) ranged between 68 and 78 g In.2 in late July in both clones (Fig. 4). SEW increased abruptly in Tristis during August, exceeding 90 g m-Z. This increase occured after budset. SEW ranged between 72 and 75 g m-2 in Eugenei throughout August and September and in- creased to above 90 g In.2 in October after budset (Fig. 4). These shifts in SEW resulted from changes in within- crown SLW patterns. On 23 July, both clones had similar within-crown SLW patterns (Fig. SB): SLWs of leaves near the apex (LPI 0) were above 58 g mm2 in both clones (since the edges of these leaves were curled, their leaf areas were underestimated using the leaf area meter and their SLWs were overestimated; significant leaf curling did not occur beyond LPI 2); SLW then declined basipetally in rapidly expanding leaves (LPI 1 to 6) of both clones; and SLW thereafter increased basipetally, reaching a maximum in the lower-crown leaves. SEW increased in Tristis during late July and August, largely due to SLW increases in its upper- and middle-crown leaves (Fig. SB). In addition, SLWs of 60 Figure 4. Changes in mean specific leaf weight (SEW) for Tristis (stars) and Eugenei (squares) trees during their first growing season. Budset dates are indicated by arrows. Each point represents the average SLW of all leaves of one tree. 61 O I I I T T I I l ‘200 210 220 230 240 250 260 270 280 JULIFlN DRYS 20 30 10 20 30 10 20 30 10 JUL AUG SEP OCT DATE 62 Figure 5. Changes in specific leaf weight (SLW) with leaf plastochron number (LPI) for Tristis (stars) and Eugenei (squares) trees for three dates during their first growing season. The location of the first mature leaf below the apex is shown by arrows. LPI 0 is the first leaf below the apex with a length :>29 mm. 63 JUL 23 03-87 mm. 0 ..E a .25m AUG 20 >§ all 2.: - -8 ..E a .23 .Av om OCT 5 also? mm. mm. .-E m .>>._m LPI 64 lower-crown leaves increased slightly during this period. In a similar fashion, SEW increased in Eugenei during late September and early October as a result of SLW increases in its upper-crown leaves (Fig. 5C). SLWs in the lower-crown of Eugenei were lower on 5 October than 20 August due to abscission of several high-SLW lower-crown leaves (Fig. SB,C). Leaflreanenlanmt New leaves matured quickly in July in both clones (Fig. 6). Mature leaves attained 20 to 25 cm2 and 30 to 40 cm2 for Tristis and Eugenei, respectively, during this period. The area of the first fully mature leaf increased with increasing tree sizein both clones (Fig. 6). The area of the first mature leaf reached a maximum when growth rates declined prior to budset. Although variation existed among trees, this maximum leaf area was 60 to 70 on2 leaf.1 and 80 to 90 cm2 leaf.1 for Tristis and Eugenei ,respectively. Total tree leaf area production in the two clones was similar up to early August (Fig. 7). Eugenei produced fewer, yet larger leaves than Tristis during this period. Leaf area production peaked in Tristis after budset at 1600 cm2 tree.1 ; leaf area peaked in Eugenei at 2850 cm2 tree-1 prior to setting bud in early September. The rate of leaf area production varied greatly throughout'the growing season in both clones (Fig. 7B). 2:! Hsiant Ilsld The hardwood cutting was the principal dry weight 65 Figure 6. Within-crown leaf area patterns for Tristis (A) and Eugenei (B) trees at four dates during their. first growing season. (The location of the first mature leaf below the apex is indicated by an arrow. LNFB : leaf number from the tree base; LA = leaf area. .66 on: mo ) LDo T a»: mu PC on»: m we m9 Wu flu 2’: W0 mo mo WU Du 60,— We m0 mo wN . wm 1m v“ 1 v z z z 10 to To c E c 70 v0 10 I I . . ’ um—E .o .0 .0 m .. .. ._ 10 1° to 9 9 9 to 0 v0 om- 2: mo I We - LOO L m I P om— LOO mo NO ON Du an: on on 0. ON w vm 1m . I 1” 1“ I a .m E v. i .meODU .0 .m < m mum m 03¢ mm .5... l m .51 9 9 9 :0 r0 r0 67 Figure 7. Total leaf area (A) and the rate of leaf area development ( ALA) (B) for Tristis (stars) and Eugenei (squares) trees during their first growing season. Budset dates are indicated by arrows. 68 —2 3000 2900 A. LEFlF HREH, cm 1000 O 80 ALA, cm2 d"1 29 / O u (USO T250 220 T 230 ' 2E0 Ezéo T 360 JULIFTN DRYS 1o 20 30 1o 20 30 1o 20 so 10 20 so JUL AUG SEP OCT DATE f 69 component in both clones during July (Table 1). The remain- ing dry matter was equally divided among the roots, leaves, and stem. As the season progressed, Eugenei increasingly partitioned its dry matter into above-ground (i.e., leaves and stem) parts whereas Tristis partitioned its dry matter more equally into above-ground and below-ground (i.e., cut- ting and roots) parts. Tristis produced more total dry matter than Eugenei through early August; however, Eugenei surpassed Tristis thereafter (Table 1). The leaf area ratio (leaf area/total dry weight), a measure of leafiness (19), was higher in Eugenei than Tristis throughout the growing season (Table 2) indicating that Eugenei reinvested a greate er proportion of its dry matter into photosynthetic tissue. In addition, Eugenei had a higher shoot-root ratio (leaf + stem dry weight / cutting + root dry weight) and harvest index (leaf + stem dry weight / total dry weight) than Tristis (Table 2). Discussion The field performance of Tristis and Eugenei was greatly affected by their respective budset dates. Eugenei more fully utilized the growing season in northern Wisconsin by extending apical growth six weeks beyond the budset date of Tristis. Pauley and Perry (23) found that the timing of budset in several E. tnlgngggngg and E. ggltgiggg clones planted in Massachusetts was directly correlated to the length of the frost-free season in the clone's native hab- itat. Differences in budset date in the present clones were Table 1. Tristis harvested per clone on 70 Dry weight (g) by date for harvested and Eugenei trees. One representative each date shown. 1-year-old tree was 9.1.922 Tristis Eugenei Comment Leaves Stem Cutting Roots Total Leaves Stem Cutting Roots Total 22x Height £31 hi DBL: 22 AUG 19 $52 5 991 23 JUN 14 17 51 12 11 34 1a 20 27 12 73 24 30 18 10 82 14 16 22 17 69 23 40 17 12 92 71 Table 2. Comparison of developmental parameters of harvested Tristis and Eugenei trees during the first growing season. DEL: 23 JUL 29 AUG 19 SEE 5 921 Glen: Trait Tristis Leaf Area Ratio 33 30 20 22 (cng-l) _ Shoot-Root Ratio“ 0.7 1.4 0.9 0.8 (s 3-1) Harvest Index" 0.4 0.6 0.4 0.4 (a 3-1) Eugenei Leaf Area Ratio 44 50 38 28 (cng-1) Shoot-Root Ratio“ 0.5 2.1 2.0 2.2 (a 3-1) Harvest Index" 0.4 0.7 0.7 0.7 (g 3'1) Shoot/Root = (leaf + stem dry wt.)/(cutting + root dry wt.) as Harvest Index : (leaf + stem dry wt.)/total dry wt. 72 likewise attributable to differences in clonal parentage. Although the exact parentage of Tristis is controversial, it did originate in the northern plains of Saskatchewan where the frost-free growing season is short, whereas Eugenei originated in the more temperate climate of France. As a result, Tristis set bud much earlier than Eugenei in north- ern Wisconsin. Therefore, Tristis and Eugenei provided a comparison between clones adapted to relatively short and long growing seasons. The pattern of leaf area development within single trees of both clones was consistent with that described by others for E. ggltglggg seedlings (2,17). Leaves produced early in the growing season mature quickly and are important sources of photosynthate for initial shoot survival and development (2,10,15). As a poplar tree grows it can sup- port a greater number of expanding leaves (2,16,17) and, as a result, each successive leaf attains greater leaf area at maturation by increasing the rate and duration of leaf expansion (17). Since Eugenei set bud much later than Tristis, Eugenei produced twenty sucessively larger leaves after Tristis ceased leaf production and attained its max- imum leaf size. Consequently, Eugenei had a larger, younger, and presumably more productive zone of large leaves than Tristis after July. Since leaf area and wood weight are highly correlated in poplar trees (10,11,18), it is reason- able to assume that the rapid total dry weight increase observed in Eugenei between August and September was attrib- 73 utable to its large total leaf area and rapid rate of leaf area expansion. In some clones, therefore, the late summer and early fall periods are important for wood production and should not be culturally ignored. The temporary reduction in leaf area expansion and height growth rates observed in Eugenei during early August was correlated with moderately low soil water tension and low night air temperature. Although Tristis had a similar reduction in leaf area production during this period, it was associated with budset processes rather than low soil water tension. Water stress has been shown to adversely' affect leaf production in several crops (1,9). It is possible that the high shoot-root ratio developed by Eugenei predisposed it to water deficits. SLW has been associated with productivity in 222312: (5,6,22) and other species (15,24). SLW patterns within trees changed dramatically in both clones throughout the growing season. Increases in SLW occurred as leaves at- tained maturity and as mature leaves aged. A portion of this increase in SLW may have resulted from continued devel- opment of leaf thickness after leaf expansion ceased (25). Increases in SLW as leaves aged may also be due to retention of .current photosynthate in mature leaves (20), adsorption and retention of calcium and other mineral elements (26), or shrinkage (7). Changes in SLW with leaf ontogeny and tree phenology must be considered when SLW is used as an indicat- or or predictor of photosynthetic potential or yield. 74 Failure to recognize that several leaf populations exist within poplar trees could result in erroneous clonal compar- isons and yield predictions. The harvest index of a plant is an indication of how effectively dry matter is partitioned into usable compo- nents. In contrast to Tristis, Eugenei invested a larger proportion of its dry matter into additional photosynthetic tissue and stem growth throughout the growing season, resulting in a higher harvest index. Isebrands and' Nelson (12) recently analysed these growth patterns and found that Tristis exports appreciable quantities of photosynthate to the roots and cutting after budset. Therefore, the roots and cutting comprise the most active sinks for photosynthate in Tristis for nearly half of the first growing season. In contrast, Eugenei exports photosynthate for stem and leaf development throughout most of the growing season (11,12,13). The growth patterns described above represent genetic adaption to growing seasons of different lengths. Tristis, which appears adapted to a relatively short growing season, concentrated its height growth into the first few weeks of the growing season in northern Wisconsin. Thereafter, dry matter was allocated for root and cutting development. In contrast, Eugenei, which is adapted to a longer growing season, more fully utilized the growing season for leaf area and shoot development. Both growth patterns have advantages and disadvantages. The extensive root system produced by 75 Tristis may enable it to grow under droughty conditions and may facilitate rapid growth in subsequent growing seasons. However, it is questionable whether such extensive root development is an economically desirable trait for SRIC trees grown under irrigated conditions. Clones such as Eugenei that have rapid and prolonged shoot growth rather than extensive root development are more suitable for the SRIC system. Full utilization of the growing season for shoot growth is an important trait for SRIC trees if maximum yields are to be obtained. However, a balance between shoot and root development is important, especially under drought conditions. 76 References 1. Boyer, JS (1970) Leaf enlargement and metabolic rates in corn, soybeans, and sunflower at various leaf water potentials. Plant Physiol 46:233-235. 2. Dickmann, DI (1971) Photosynthesis and respiration by developing leaves of cottonwood (£92319; ggltgidgg Bartr). Bot Gaz 132:253-259. 3. Evans, LT (1975) The physiological basis of crop yield. - In Evans, L, ed. Crop physiology - some case hist- ories, pp.327-355. Cambridge, Cambridge Univ Press. 4. Farmer, RE (1979) Yield components in forest trees. In Hollis, CA, AE Squillace, eds. Proc Fifth North Amer Forest Biol Workshop, pp.99-119, Gainesville, Florida. 5. Furukawa, A (1973) Photosynthesis and respiration in poplar plant in relation to leaf development. J Jap For Soc 55:119-123. 6. Gottschalk, KW, DI Dickmann (1978) First year growth, biomass yield, and leaf area development of four intensively-cultured £92312; clones in southern Michigan. In Pope, PE, ed. Proc Central Hardwoods For Conf II, pp. 140-158, West Lafayette, IN. 7. Hackett, C (1973) An exploration of the carbon economy of the tobacco plant. I. Inferences from a simula- tion. Aust J Biol Sci 26:1057-1071. 8. Hansen, EH, H McNeel, D Netzer, H Phipps, P Roberts, T 9. 10. 11. 12. 13. 14. 77 Strong, D Tolsted, J Zavitkovski (1979) Short rotat- ion intensive culture practices for northern Wisconsin. Proc 16th North Amer Poplar Council, pp.47-63, Thompsonville, MI. Heatherly, LG, WJ Russell, TM Hinkley (1977) Water relations and growth of soybeans in drying soil. Crop Sci 17:381-385. Isebrands, JG (1982) Toward a physiological basis of intensive culture of poplars. Proc 1982 TAPPI Res & Devel Conf, pp. 81-90, Asheville, NC. Isebrands, JG, ND Nelson (1980) Photosynthate distribution within short rotation intensively cul- tured Populgs clones during the establishment year. Proc North Amer For Biol Workshop, p.150, (Abs) Edmonton, Alberta, Canada. Isebrands, JG, ND Nelson (1983) Distribution of 1“C- labeled photosynthates within intensively cultured figpglgg clones during the establishment year. Physiol Plant 59:9-18. Isebrands, JG, ND Nelson, DI Dickmann, DA Michael (1983) Yield physiology of short rotation intensively cultured poplars. In Hansen, E, ed. Intensive plant- ation culture: 12 years research, pp.77-93. USDA For Serv Gen Tech Pap NC-91. Kallis, A, H Tooming (1974) Estimation of the influence of leaf photosynthetic parameters, specific leaf weight and growth functions on yield. Photosynthetica 15. 16. 17. 18. 19. 78 8:91- 103. Larson, PR (1974) The upper limit of seedling growth. Great Plains Agric Council Pub No 68. ' Larson, PR (1980) Interrelations between phyllotaxis, leaf development and the primary-secondary vascular transition in Populgg ggltglggg. Ann Bot 46:757-769. Larson, PR, JC Gordon (1969) Leaf development, photosynthesis, and 1“C distribution in Egpglgg ggltglggg seedlings. Amer J Bot 56:1058-1066. Larson, PR, JG Isebrands (1972) The relation between leaf production and wood weight in first-year root sprouts of two Egtglgg clones. Can J For Res 2:98- 104. Ledig, FT (1974) Concepts of growth analysis. In Proc Third Amer For Biol Workshop, pp. 166-182, Ft. Col- lins, CO. 20. Nelson ND, JG Isebrands (1983) Late-season photosynthe- 21. sis and photosynthate distribution in an intensive- ly-cultured £92213; nigzg x lgnnifglig clone. Photo- synthetica (In press). Nichiporovich, AA (1966) Aims of research on the photosynthesis of plants as a factor in productivity. In Nichiporovich, AA, ed. Photosynthesis of product- ive systems, pp. 3-36. Translated from Russian by Kaner, N (Monteith, JL, translation ed.), Jerusa- lem, Israel Program for Scientific Translations, 1967. 22. 23. 24. 25. 26. 79 Okafo, 0A, JW Hanover (1978) Comparative photosynthesis and respiration of trembling and bigtooth aspens in relation to growth and development. For Sci 24:103- 109. Pauley, SS, T0 Perry (1954) Ecotypic variation of the photoperiodic response in 292313;. J Arnold Abor 35:167- 188. Pearce, RB, GE Carlson, DK Barnes, RH Hart, CH Hanson (1969) Specific leaf weight and photosynthesis in alfalfa. Crop Sci 9:423-426. . Pieters, GA (1974) The growth of sun and shade leaves of Populus guzameztcggg 'Robusta'in relation to age, light intensity and temperature. Mededel: Landbouwho- gesch. Wageningen 74-11:1-106. Zelawski, W, RB Walker (1976) Photosynthesis, respira- tion, and dry matter production. In Miksche, JP, ed. Modern methods of forest genetics, p. 288, New York, Springer-Verlag. CHAPTER III CHARACTERIZATION OF PHOTOSYNTHESIS WITHIN TWO FIELD-GROWN EQEHLES CLONES DURING THE ESTABLISHMENT YEAR Prepared for Submission to PHOTOSYNTHESIS RESEARCH 80 81 Abstract. Diurnal and seasonal photosynthesis patterns were established for two Populus clones during their first field season using a 1“CO device. Photosynthetic rates were low in immature leaves? increased basipetally and peaked in recently-mature leaves;, and thereafter declined in lower- crown leaves in both clones. Photosynthesis was strongly associated with leaf age and stomatal conductance in im- mature leaves; adaxial irradiance and leaf temperature in recently-mature leaves; and leaf age and adaxial irradiance in lower-crown leaves. Diurnal photosynthesis patterns within trees were highly variable due to differential light interception between leaves. Results of clonal comparisons of photosynthetic rates were dependent upon which leaves were pooled for comparison and how photosynthesis was expressed. Tristis (E. tnigtig x B. balsamifsna) produced smaller leaves which had higher unit-area photosynthesis rates than Eugenei (E. x ggngmgniggng) which produced larger leaves which had lower unit-area photosynthesis rates. Eugenei outgrew Tristis principally by fully utiliz- ing the growing season for leaf area production. Photosyn- thetic production integrated over the growing season closely matched dry matter production in both clones. 82 Introduction A major goal in forestry research is to develop proced- ures to predict yield. To achieve this goal, plant and environmental factors,that influence and control yield must be fully understood. All factors which influence yield must do so by directly or indirectly influencing photosynthesis or photosynthate distribution (39). Therefore, a thorough understanding of the photosynthetic process under‘ field conditions is required if yields are to be reliably predict- ed. A logical approach for investigating photosynthesis is to develop baseline data under controlled environmental conditions, test this data through field experimentation, and then refine concepts developed in the field with further controlled- environment work (27). This approach has been used to examine the photosynthetic physiology of Egpnlng species. Early controlled-environment work established baseline physiological data for young poplar trees (4,5,7,19,28,31). As a logical extension of this work, field experiments were conducted to examine growth, CO fixation, and dry matter distribution in two hybrid poplai clones during their first growing season. Growth and dry matter distribution have been described in earlier papers (20, Chapter II). The objective of the present study was to characterize photosynthesis within two field-grown hybrid poplar clones and determine how much CO was fixed, where it was fixed, 2 . 83 and what were the major factors influencing CO fixation. 2 More specifically, our intent was to quantify diurnal and seasonal, changes in single leaf and whole-tree photosynthe- sis throughout the first growing season. Methods and materials Plant Mategial. Two hybrid poplar clones, figpglgg x euramericagg cv. "Eugenei" (NC 5326) and 2. tglgtig x P. balsamifera cv. "Tristis #1" (NC 5260) (hereafter, Eugenei and Tristis, respectively) were grown under a short-rotation intensive culture system (14). The trees were established on May 22, 1979 at the U.S. Forest Service's Harshaw Experi- mental Farm near Rhinelander, Wisconsin (U.S.A.) using 1,040 25 cm unrooted hardwood cuttings per clone. Cultural treat- ments have been described in an earlier paper (Chapter II). 1n 1" £9 Teehniaee and Cemsanien Measurements. The co 2 2 technique described earlier (Chapter I) was used to measure photosynthesis in the field. Briefly, the technique involv- 2 ed exposing a 0.95 cm section of leaf lamina located midway 3 -3 1 between the leaf tip and base to 322 cm m of CO - -1 2 labelled air with a specific activity of 185 kBq l (at 21 o C and 1 atm.)(Matheson Gas Products) for 20 s at a constant -1 flow rate (1.3 ml 5 ) and then subsampling the exposed section with a sharp #4.cork borer (diameter = 7 mm). After excision, the leaf disk was placed into a 20 ml scintillat- ion vial containing 1.5 ml NCS tissue solubilizer 84 (Amersham/Searle). In the laboratory, 1.5 ml 6f 0.51 benzyl peroxide was added to each vial and the disks were digested o for 24 h in an oven at 50 C. After the digestion period, three drops of glacial acetic acid and 13 ml of scintillat- ion cocktail containing 63 ml of Spectrafluor (Amersham/Searle) in 1 l toluene were added to the vials. The vials were placed in a darkened chamber for 3 h to reduce chemilluminescence and were then counted with a liquid scintillation spectrometer (Beckman model LS 150). Photosynthetic rate on a unit area basis (PgA, mg C0 m 2.1 2 s ) was then calculated from: PgA (CPM/CE x CCO x 1.18)/(SA x LA x T) 2 where: CPM sample counts per minute (corrected for back- ground radiation); CE : counting efficiency of the liquid scintillation spectrometer (expressed as a decimal); CCO -1 2 = concentration of CO (mg CO 1 ) at a standard tempera- 2 2 ture and pressure (determined in our case from Matheson's calibration); 1.18 = a discrimination factor to account for diffusive and biochemical discrimination against 1“C0 (1,43); SA = the specific activity of the 1“CO ~1ZCO gas mixture at the same standard temperature and presiure a: in CCO (dpm 1.1 gas mixture); LA = the area of the excised lea? disc (m2); T = length of the 1“C02 pulse (3). Experi- ments conducted in 1979 and 1980 indicated that photosynthe- 14 sis rates measured by the CO technique exceeded those 2 measured by an infrared gas analyzer by ca. 5 percent; 85 however, there was not a significant difference between the two methods (P s 0.05) (Chapter I). Several companion measurements quantified the condition of the leaf and environment during the photosynthesis meas- urement. These were: 1. Photosynthetically active photon flux density (PPFD, u mole m-Zs-1, 400 to 700 nm) - measured normal (i.e., perpendicular) to the adaxial (PPFD ) and abaxial (PPFD ) leaf planes and also above and belgg the tree crown usinéBa LiCor model LI-185 meter and quantum sensor (hereafter, the terms "PPFD" and "light" will be used interchangeably). All leaves were measured in their natural orientation. 7 2. Diffusive resistance to H 0 (s mm-1) - measured with a LiCor model LI-65 autoporometir and horizontal sensor (24) on the abaxial leaf surface. Both clones were amphi- stomatous, but with fewer stomata on the upper than lower leaf epidermis. . 3. Leaf temperature (LT, oC) - measured by apressing a YSI model 427 stainless steel thermistor against the abaxial leaf surface. Air temperature was measured as above approx- imately 5 cm below the abaxial leaf surface in the shade of the leaf. 4. Relative humidity (1) - measured within the crown of each tree using an American Instrument Co. hygrometer and appropriate narrow range humidity sensor. 5. Leaf orientation - measured for selected leaves using a weighted protractor (34). 86 After completion of all daily field measurements, three leaves at each of four crown positions (see below) were excised and their petioles placed immediately into scintil- lation vials containing 15 ml distilled water. CO2 compen- 3 -3 sation points ( r , cm m CO ) were measured in the lab- 2 oratory by placing each leaf into a mylar bag inflated with 3 -3 0 air containing 350 cm m CO (6) (LT: 27 C, PPFD =660 u -2 -1 2 AD mole m s ). After one hour the contents of the bag were expelled through an infrared gas analyzer (Beckman model 215A) and P was determined. Unpublished experiments con- ducted in 1978 indicated that compensation points of leaves- treated in this manner were not significantly different from those determined on leaves in gitn. Each sampled leaf was excised and its area measured with a leaf area meter (Lambda Instruments model LI-3000). Leaf dry weight was then determined by oven-drying the 0 leaves at 100 C for 24 h and weighing the samples on a Sartorious balance. Calculatgd Panamgtgzs. Several parameters were calculated from the measured variables. These were: (1) specific leaf -2 _ weight (SLW, g m ), (2) photosynthesis on a unit dry -1 - weight basis (PgW, mg CO g s ), (3)1photosynthesis on a 2 1 whole-leaf basis (PgL, ug CO 3 leaf ), (4) whole-leaf 2 light interception (photosynthetically active photon flux -1 (PPF, u moles 3 leaf )), and (5) stomatal conductance to -1 CO (CON, mm s ) calculated from: CON = (1/r) x 0.623, 2 where 0.623 is the ratio of diffusion coefficients for CO 2 87 and H O in air (21). In addition, effective PPFD (PPFDe, u molesZm-Zs-1) was calculated from: PPFDe = PPFD + (PPFD x e), where e is a conversion factor to adjugg for t3: different effeciencies of abaxial and adaxial light in driv- ing photosynthesis.w e has not been experimentally deter- mined for poplars, therefore, 0.5 was selected after reviewing our data and data presented by others (36). Also, light-use efficiency (LUE, mg CO2 per u mole incident PPFDe). was calculated from: LUE : PgL/PPF. Samplg Iggg Sglggtign. Measurements from a permanent growth plot located within the main plantation were used to guide selection of sample trees. Twenty-four trees per clone spaced evenly over the plantation were measured weekly to obtain estimates of mean tree height, total number of leaves, and stem diameter. At each photosynthesis sampling date, trees which represented the average of these measure- ments were selected from the main plantation. This assured that "average" trees in the plantation were sampled at each measurement date. An "average" tree was defined as a tree whose height and total number of leaves approximated the plantation mean. Photosynthgsig Measuremgnt . Diurnal photosynthesis pat- terns were established for four crown regions, comprising two oblique age series and one horizontal age series (5, Chapter I). The first oblique series, A, was located in the upper crown (i.e., leaf plastochron index (LPI) 3 (29)) and 88 consisted of an immature leaf (i.e., expanding) prior to budset. After budset, leaves in the A region were morpho- logically mature (i.e., not expanding). The second oblique series, B, was located in the upper-middle crown and consisted of a recently-mature leaf. Prior to budset, B was the first fully mature leaf below the apex; after budset , B was standardized at LPI 9. The third oblique series, C, was located in the middle-lower crown and was a leaf which had reached maturity several days prior to measurement. The C leaf was the central leaf between the B and D leaf posit- ions. The horizontal series, D, was a lower-crown leaf which attained maturity early in the growing season. The D leaf was the sixth leaf up from the lowermost leaf. Succes- sive daily leaf length measurements ensured that this sampl- ing pattern was maintained throughout the growing season. Since the 14C0 device measured a portion of the leaf lamina destructivelyf photosynthesis was not measured on the same leaf at each crown position throughout the day. In- stead, measurements were taken at the four crown positions on leaves from similar trees. Two leaves per position per tree were measured during the diurnal period. For example, if the diurnal measurement consisted of eight sample periods (i.e., one measurement every two hours from 6 am to 20 pm solar time (ST)), then four trees per clone were selected as sample trees.) Within each sample tree, two adjacent leaves were selected at each crown position. One tree and one leaf per position were selected randomly from this pool for each 89 two-hour measurement. One tree per clone was selected on six different dates and the photosynthetic rate of each leaf determined. These entire-leaf series measurements began at 10 am (ST) to avoid possible midday photosynthesis depressions. Boundary Ltne Agglygtg. Boundary line analysis (18,46,0hap- ter I) was used to establish response curves for the meas- ured variables. All measured values for several two- variable combinations were plotted and least-squares lines were established through the exterior points using linear or non-linear regression (Chapter I). These lines represented the limiting effect of the independent variable on the dependent variable; it was assumed that points below the boundary lines resulted from the influence of another unplotted variable or combination of variables (18). Field and laboratory tests have shown that the boundary line technique provides reliable response curves for the PgA/PPFDe relationship (Chapter I). Intggcgtign gt fingtggyntnggig. An estimate of the daily total carbon uptake of each leaf within a tree was obtained from the diurnal photosynthesis measurements using the mea- sured leaves within each crown section to estimate PgA for unmeasured leaves. PgA rates were averaged within each measurement period for each crown region, e.g., if three leaves were sampled in the A crown region between 7 and 8 am (ST), then the average of their PgA rates was used as the 90 7:30 am PgA rate. For each measurement period within a day, average PgA rates were plotted against LPI and smooth curves were established through the points. These curves were used to estimate PgA rates of unmeasured leaves. Whole-leaf photosynthetic rates were then calculated. The photosynthe- tic output of each leaf during the measurement period was calculated by multiplying each leaf's whole-leaf photosyn- thesis rate by the number of hours between measurement periods (in most cases, two hours). Photosynthesis was integrated in this manner for a 14 hour diurnal period, beginning at 6 am and ending at 20 pm (ST). Integrations were performed for four sunny-day diurnal measurements to obtain estimates of total daily carbon fixation (TDCF, mg CO tree.1 day-1). The growing season was then divided inEo four periods and these TDCF values were used to esti- mate TDCF for all sunny days (radiant flux density 97 Wm- 2) within each period. One-half of the sunny day TDCF was used as an estimate of cloudy day performance. The total photosynthetic output of both clones between 28 May 1979 and '10 September 1979 was then estimated. These data were then used to estimate cummulative TDCF for days which whole trees were harvested and their component dry weights determined (Chapter II). The dry-weight equivalent of cummulative TDCF was estimated using 1.63:1 as the ratio of g CO fixed to g 2 . carbohydrate produced (2). Growth Analysis Hanvgst . "Average" trees (one tree per 91 clone per date) were periodically harvested and the dry weight of their leaves, stem, cutting, and root determined (Chapter II). "Average" trees were selected using data from the growth plot as guidelines. Results Expression ghg Comhahison g; Phgtosyhthehig gages. Compari- sons within and between clones were influenced by how photo- synthesis was expressed and by which sets of leaves were compared. To illustrate, photosynthesis was expressed on a unit area, unit dry weight and whole-leaf basis and com- pared between clones using different sets of "similar" leaves for the 30 August 1979 entire leaf series measurement (Fig. 1). "Similar" leaves were selected using similar LPIs, similar crown regions or strata, and similar leaf numbers from the base of the crown (LNFB). When LPI was used to identify "similar" leaves, PgA rates in Eugenei surpassed those in Tristis in the LPI 11 to 20 and 21 to 30 leaves, however, PgA rates were greater in Tristis than Eugenei in the LPI 0 to 10 leaves (Fig. 1C). When expressed as PgW, photosynthesis was similar between clones in the LPI 0 to 10 leaves and differences were accentuated in the LPI 11 to 20 and 21 to 30 leaves. PgL rates in Eugenei were greater than those in Tristis in all leaves (Fig. 16). When "similar" leaves were selected 92 Figure 1. Expression of photosynthetic rates on a unit area (PgA), unit weight (PgW) and whole-leaf (PgL) basis for Tristis (squares) and Eugenei (stars) leaves measured 30 August 1979. Leaves were pooled for comparison by leaf number from the tree base (LNFB) (A), crown section (B), and leaf plastochron index (LPI) (C). -93 \ \ \ & u-|1| 14,. 1.. I 4 Q 4 4 001:. 97...». onl—N owl: o—lo _ 11-1411 4 I? * omlpv oelwn onlpm owl: O—Io «1 4| 4) 4 4 on]; 91:, onlm 8:: 070 mmzb fie — ”'1 ’d 8 4 .1 a a 4 0 P N n v 0 j C 1 8 0 6 r . 0 4 0 2 1' I 0 0 <11 a A 4 . 0 F N n v ZO;omm ZBOmo } Put (#900234) « «1 a J a 07.0 0N1: Pnlpm oelfin owl; o—lo 0N1: PHI—N Otl—n owl; I r r r V q‘ a A J 4 0.10 own: Pnlpm eel—n owl; .m4 0.0 0.2 0.4 0.6 0.81.0 PgW (urngozmg'l'sfl) PgA OngCOgnqs”) 94 'using crown regions or vertical strata (Fig. 18) (each crown region comprised 25% of the total number of leaves) photo- synthesis was higher in upper leaves of Tristis than Eugenei when expressed as PgA but not when expressed as PgW or PgL; photosynthesis rates were greater in Eugenei than Tristis in the second crown region, regardless cf how it was expressed; photosynthesis rates were similar in region #3; and photo- synthesis rates in the lowest leaf region of Tristis (#u) surpassed those in Eugenei, regardless of how expressed. When similar-aged leaves were compared by grouping leaves acropetally (Fig. 1A),‘ Tristis lower leaves (LNFB O to 20) had higher photosynthetic rates than Eugenei lower leaves, however, LNFB 21 to no Eugenei leaves had equivalent or higher photosynthetic rates than Tristis leaves in the same region. Tristis did not have leaves in the LNFB #1 to 50 region for comparison. Photosyhthesis Within ihgiyidual Ihggs. Both clones were in a similar stage of growth during the 10 July 1979 entire leaf series measurement, i.e., a new 30 cm leaf was produced by the apical meristem on ca. two day intervals; height growth was proceeding at a rate of 1.5 cm d- ; and both clones had ca. 8 expanding and 12 mature leaves (Chapter II). Within-tree PgA patterns were also similar between clones during this period (Fig. 2): rapidly expanding leaves near the apex had low PgA rates regardless of microenviron- ment; PgA increased basipetally in the rest of the expand- ing leaves and peaked in the last expanding or 95 Figure 2. Photosynthesis (PgA) by leaf number from the tree base (LNFB) for three measurement dates on which each leaf within each Tristis (squares) and Eugenei (stars) tree was sampled. ,% Br / 1.: .l. 1. . 10 1.111 ‘1‘“.3 a): 9.4.. (I 3.}! , .19 3 511.1% a 10 ‘133 31:111.. w. J. 8 1.23‘“' 1.0 1.: .1 .V r0 9 . IO mumF OD< on out: .8 95 <3 P mmmr OD< m N; one To 0.9”. . Ll QAQF 43w 0— 97 Have» no acoogoa mom momosusogmn ca mosam> m onus mug» scam cones: mama u mmzq F m.mm MM! mp: Mm qmm4 . mmzq meoao m m N F mama .mhmp aasa op nossmmoa manages new accomsm Lou Amaqv hocoaofimuo on: anwfia new .Aammv mfimospcznOpona mmoaloaosz .Ammmv asam second m>auomuaaamouuosacanouonq .mogm mama Hugo» mo comagmasoo czogoncanuaz .P manna 98 first mature leaf; and PgA then declined basipetally in the lower-mature leaves. Although both clones had similar within-crown PgA pat- terns on 10 July 1979, differences existed in whole-tree carbon fixation (Pg , ug CO 3-1 tree-1) and whole-tree tot 2 -1 -1 light interception (PPF , u moles 3 tree ) (Table 1). Both clones interceptedtgter 60% of PPF and fixed ca. 60% of Pg in the upper crown region; h0325er, Eugenei Pg tot tot surpassed Tristis Pg by “1% on 10 July 1979, largely due to 33% greater leaf :::a in Eugenei in the upper region. Prior to setting bud on 30 July 1979, Tristis had a more rapid rate of height and diameter growth than Eugenei. After budset, leaf initiation and significant leaf expansion ceased. As a result, Tristis leaves were morphologically mature and its leaf area and total number of leaves were fixed until leaf abscission began in mid-August. In con- trast, Eugenei maintained leaf production until setting bud on 10 September 1979. Nine of 33 Eugenei leaves were im- mature on 8 August 1979 (Chapter II). The 8 August 1979 entire leaf series measurement (Fig. 2), therefore, compared trees with similar physical but different phenological char- acteristics. The general within-crown photosynthesis pat- tern described for the 10 July 1979 entire leaf series measurement was observed on 8 August 1979 (Fig. 2). As the trees grew, the size of the immature and recently-mature leaf zones and the average area of individual leaves in these zones increased (Chapter II). Therefore, each clone 99 aauou mo ucmogma mga amamnucmgaa ca amsaa> m mnan mmmu scam cmnszz mama u mmzq m.=m mm: 553., wm 4. Acme om A_av opm o. o.-. ¢.o Ammo o..m Ammo am Ammo am: a omupp o.. Amav o.am Ammo mm Away mac o. omspm m.o A. V m.o APV F may mm a amnpm Hmcmmsm o.am mww amm.. mm 4aoq mmzq ocoao a a a P mama .msm. unam=< m cmgsaama mammaza aca amcmmsm mom Amaqv mocmaoammm ma: unmaa uca .aqmmv nanmnucaaouonq mamaumaosz .Ammmv usam :ouona m>auoalaaaaOaumsucanouoza .amga mama aauop mo coaagaqeoo czozoucasuaz .N manah 100 had a broader plateau of leaves with high PgA rates on 8 August 1979 than on 10 July 1979 (Fig. 2). PgA rates were higher in Tristis than Eugenei in the upper crown on 8 August 1979 (Fig. 2), but Pg was sim- ilar for the two clones (Table 2). Eugenei comgggsated for its lower PgA rates by producing larger leaves than Tristis. Overall, Pg was 51 greater in Tristis than Eugenei on 8 August 1979.t3§permost leaves in Tristis were morhpological- 1y mature, however, they did not attain PgA rates equivalent to leaves which matured before budset. However, those upper leaves had higher PgA rates than leaves at similar positions measured before budset (Fig. 2) and their PgA rates were higher than Eugenei upper leaves. Tristis surpassed Eugenei in Pg on 8 August 1979 largely due to greater product- ivity ggtits upper leaves. The two clones had roughly equal PPF on 8 August 1979, but light interception in Tristis wastggncentrated in its upper crown while in Eugenei, light was distributed more evenly (Table 2). Light was utilized with different effeciencies within trees and between clones. LUE's were highest in the lower-crownregion of Tristis, indicating that its older leaves responded well to low light levels. In contrast, LUE's peaked in the upper-middle crown region of Eugenei and declined basipetally. Terminal buds had been set for 30 days in Tristis by the time of the 30 August 1979 entire leaf series measure- ment (Fig. 2) and its leaf area did not increase between 8 August 1979 and 30 August 1979. Rather, abscission of four 101 lower-crown leaves had reduced its leaf area by about 10%. Eugenei was still producing new leaves on 30 August 1979, but leaf initiation rates were declining and budset occurred 10 days later (Chapter II). The Eugenei leaf complement consisted of 8 expanding and 29 mature leaves on 30 August 1979. Seven lower-crown leaves had abscised (1H1 of to- tal). The more indeterminate growth pattern of Eugenei produced a Hui leaf area advantage over Tristis on 30 August 1979 (Table 3). This leaf area difference produced compar- able differences in PPF (u1z) and Pg (44%) between - tot tot ‘ Eugenei and Tristis. The lower-crown regions in Eugenei were less productive on 30 August 1979 than on 8 August 1979 due to leaf aging and abscission. However, this loss in productivity was compensated for by the addition of younger, larger leaves in its upper-crown. The lower-crown region in Tristis received more light on 30 August 1979 than on 8 August 1979 (Tables 2,3) because the sampled tree was in- advertently selected near an opening in the plantation created when a neighboring tree was harvested. Thus, leaves directed towards the opening received full sunlight. Tristis lower-crown leaves responded to this increased light with a higher Pg than measured earlier. However, reduced tot LUE's indicated that much of the additional light was used inefficiently. QQ Compengation Pgint. F ranged from 56 to 95 and 65 to 2 3 -3 92 cm m in Tristis and Eugenei mature leaves, 102 aauou mo unmogmn mga mmamnucmgaq ca amsaa> N 0me OULQ EOLM L0983: MNOH u mhzq 0.0mm mmm 0mm.a mm 0am4 mmzq mcoao N N N F mama .msmp uazms< om cmgsaams aaaaaua uca amcmmsm com Amaqv mocmaoammm ma: unmaa aca .Aqmmv aaamsuzmaouona mamaumaosz .ammmv xsam :ouona m>apoaumaaaoaumsuczaouosa .amga mama aauou mo :oaagaasoo czoeoucasuaz .m manaa 103 -3 -2 Table u. C0 compensation points (cm m ) for varoius 2 leaf positions for Tristis and Eugenei trees by date. Each value represents the average of three determinations. Leaf Date 'Clone Position 7 Jul 20 Jul 15 Aug 29 Aug 8 Sep -3 -2 cm m Tristis A -- -- 61 57 55 B 56 70 58 57 55 C 56 70 57 56 60 D 63 73 58 85 95 Eugenei A -- -- 227 191 85 B 72 76 70 80 72 C 92 85 70 70 75 D 65 70 72 73 70 10“ respectively (Table u). Mean T's were significantly lower in Tristis than Eugenei in the A and pooled B and C regions, however, no difference existed in the D region means. I‘ was highest in the immature Eugenei leaves, although it declined in those leaves as the season progressed. A slight P increase was observed in lower Tristis leaves but not in Eugenei lower leaves as the season progressed (Table u). Engihgnmghhgi Effigggh 9h fihggggynfihgfiis. Light saturation was reached at ca. 1100 and 1700 u moles muzs-1 for Eugenei and Tristis leaves, respectively (Fig. 3C). Although LUE's were similar at all leaf positions, the PgA rate at saturat- ing PPFDe (Pmax) varied markedly in both clones (Fig. 30). Both clones had the same photosynthetic response to leaf temperature (Fig. 3B). PgA increased linearly with increasing LT at all leaf positions reaching a maximum near 25 oC and 30 0C for Eugenei and Tristis, respectively. Temperature optima are uncertian since leaf temperatures 0 rarely exceeded 32 C. Stohatgl Qghghgfighgg. Photosynthesis increased linearly with increasing conductance at low conductance levels (below 0.8 mm s-1) in both clones (Fig. RC). Photosynthesis reach- ed a plateau (Pmax) at conductance levels above 0.8 mm 3-1. Pmax and the rate at which Pmax was approached (<1) varied within and between clones. The upper leaf position (A) in Tristis had the highest Pmax and steepest <1 ; Pmax and a declined basipetally within Tristis. The same trend 105 Figure 3. Boundary line plots of photosynthesis (PgA) ver- sus photosynthetically-active photon flux density (PPFD) (B) and leaf temperature (LT) (A) for Tristis and Eugenei leaves at various positions within the crown. Only data near the boundary lines are shown. Stars (A) = immature leaf; cir- cles (B) = recently-mature leaf; asterisks (C) = leaf in center of mature leaf zone; triangles (D) = lower-crown mature leaf. 1.2 PgA (mg CO2 mas") 1.2 (9.0 0.4 0.8 0.8 PgA (mg CO2 m’23'1) 0.4 c9.0 106 TWSWS 0 '1 l o. ”I 0 A d . '. 6 .‘ 00 o o A .‘l d ‘ ‘ m 0‘” 1 l r T fl 8 16 24 32 LT (°C) 0 a 0‘ . O 0:; ‘03. *0 A d . . ‘ 09“. x? 1 Sir“ 800 1é00 2100 PPFDe (,(Lmole m'zs") 0.8 .4 0 9 ‘% EUGENE o, i 1 0... GD , A. 0° ‘ i a! ‘t a; 0‘ x J41 l 1 8 16 24 32 LT (°C) ! o i"0 m 00 (D (D ‘ A (59. A ‘. a A o t . y. C) B Q: 316 C r M it 800 Iéoo 2200 PPFDe (“mole mas") 107 Figure u. Boundary line plots of photosynthesis (PgA) ver- sus stomatal conductance (CON) (C), stomatal conductance versus photosynthetically-active photon flux density (PPFDe) (B), and stomatal conductance versus leaf temperature (LT) (A) for Tristis and Eugenei leaves at various locations within the crown. . Only data near the boundary lines are shown. Stars (A) = immature leaf; circles (B) = recently- mature leaf; asterisks (C) : leaf in center of mature leaf zone; triangles (D) = lower-crown mature leaf. 1.0 1.5 2.0 CON (mm s“) c9.0 0.5 2.0 1.5 1.0 CON (mm s") c9.0 0.5 108 TREHNS ’ 9% I 1“; 8' 16 T 800 1000 2100 PPFDe (pmole m'zs") 7M: .8 N "‘ .0 . o I . I Em C .0. A a; - 0 °?. I CE“? 3 v0 . < : EC: ‘0.0 0.5 1.0 1.5 2.0 CON (mm s") EUGENEI (<11 ”3 Ilsa .—.. I a “ . C3. 0.0 H C an L0 .J ‘. 0 t 0. C? C0 8 16 24 32 LT (°C) C? N1 1 0‘ a O . . :3 .‘ f o o ° . ' o "‘ 9. ”3 O ‘9 ‘0 800 1500 2300 PPFDe (umole m”s") 0% I (D 0 ° :0. 0. . s 09.: 0 0‘ °:‘ "‘ Al A :3. (3.1;! r 1 l c0.0 0.5 1.0 1.5 2.0 CON (mm s") 000) 109 was observed within Eugenei; however, its A leaf had a lower Pmax and flatter a than Tristis. Tristis a's were steeper than similar leaf positions in Eugenei. Conductance increased rapidly with increasing light in leaves of both clones (Fig. as). The slope of the CON/PPFD curve at low light levels was flattest in Eugenei upper and lower leaves (A and D) indicating that stomata in those leaves were less responsive to light fluctutions than other Tristis and Eugenei leaves. Tristis leaves attained higher CON rates at light saturation than Eugenei leaves, but the rate at which this maximum was approached was similar for the B and C leaf positions in both clones. CON measurements at low light levels are absent from our data since stomatal resistance could not be measured in early morning with the porometer due to water condensation on the leaves. As a result, threshold levels for stomatal opening could not be determined. CON increased rapidly in response to increasing leaf temperature in all leaves (Fig. HA). The response of CON to LT was the same in all Tristis leaves. Some differentiation occured in Eugenei: CON rates responded rapidly to LT in mature mid-crown leaves (B) and slowly in immature upper- crown leaves (A). Intehhelatignships Between yghiabies. PgA increased linear- ly in the uppermost leaves of both clones (Fig. 5) and was strongly correlated with CON and LPI (Tables 5,6). CON and LPI were strongly intercorrelated in those leaves. PPFDe 110 Figure 5. The relationship between leaf number from the tree base (LNFB) and photosynthesis (PgA), photosynthetic- ally-active photon flux density (PPFDe), stomatal conduct- ance (CON), and leaf temperature (LT) for each leaf on single Tristis and Eugenei trees measured 30 August 1979. LNFB LNFB LNFB LNFB Ill 'WNSWS Q. U) 04 0, c). m (3‘ N 01 "0 81 10 21 30 LT (°C) 31 Q-A V Q. m (:34 N 94 C0.0 0T.s 1T.0 1:5 210 CON 0nn1s”) C) U) o. i o. ;,:<_.:. m - 04 - 8‘ N 3. 0" i 91 800 1000 2:100 PPFDe (hmole m'zs") 0. LO D. V o. m Dd N 01 (21.0 0:5 1:0 13 PgA (mg CO,m"s") riO'H: 1. L 10 20 30 40 5 1 1W LT (°C) 0. LD Ca V 81 c). N o. c0.0 0:5 1T0 115 7.0 CON 0nn1s”) c). ”’ ; (2)-1 v v -:E§EE__==’ 31 , 1 0+ N 01 C0 800 1000 7400 PPFDe (,umole m"s"') 0. LD 01 Q 04 m 04 N o. 90.0 015 1:0 13 PgA (mg COzm'zs") 112 and LT were weakly associated with PgA in the_upper leaves. PgA fluctuated widely in the recently- mature leaves in response to changes in leaf microenvironment (Fig. 5). PPFDe, CON and LT were strongly associated with PgA in the recently-mature leaves,- whereas LPI had a weak association with PgA. PPFDe, CON, and LT were highly intercorrelated in both clones in those leaves. PgA in the middle-mature region was also strongly associated with PPFDe, CON, and LT in both clones, while the correlation between PgA and LPI became stronger in Eugenei middle-mature leaves. The corre- lation between PPFDe and PgA was exceptionally high in Tristis middle-mature leaves (Table 5), indicating that . light was the major factor limiting photosynthesis. LPI had a stronger negative relationship with PgA in the lower-crown leaves of both clones, especially Eugenei (Table 6). Corre- lation coefficients indicate that PgA was more closely asso- ciated with microenvironment in lower leaves of Tristis than Eugenei (Tables 5,6). Diurnal Pbcigsxnibssis Battenns. On a sunny day. PsA. LT. and CON increased linearly in early morning (6 to 8 am ST) in response to rapidly increasing light. PgA rates were similar .at all leaf positions in early morning (Figs. 6,7,8). As light levels increased in late morning, (8 to 10 am ST) PgA differences developed between leaves in accord- ance with their varying photosynthetic capacities, i.e., leaves at the B and C positions typically had higher PgA Table 5. 113 Simple correlation coefficients between photosyn- thetic rate (PgA), photosynthetically-active photon flux density (PPFD), leaf temperature (LT), stomatal conductance (CON), and leaf number from the tree base (LNFB) for leaves pooled acropetally in a 1 year-old Tristis tree measured at 10 am (solar time) on 30 August 1979. Parameter LNFB Range PPFD LT CON LNFB 20-27 11-19 8-13 1-7 20-27 11-19 8-13 1-7 20-27 1u-19 8-13 1-7 20-27 11-19 3-13 1-7 Parameter 1 PgA- PPFD LT con -053 .85 .96 - .69 -.25 .60 .82 .96 .52 .59 051 095 .140 -021 ‘026 .9“ .83 .89 .75 .85 .75 .57 .80 .89 .8“ ' '056 -016 062 .11 .59 .50 .12 .01 -009 -063 -016 -0188 -007 -012 -0u2 1 Natural log transformation of PPFD Table 6. 1111 Simple correlation coefficients between photosyn- thetic rate (PgA), photosynthetically-active photon flux density (PPFD), leaf temperature (LT), stomatal conductance (CON), and leaf number from the tree base (LNFB) for leaves pooled acropetally in a 1 year-old Eugenei tree measured at 10.50 am (solar time) on 30 August 1979. LNFB Parameter Parameter Range PgA PPFD LT CON PPFD 01-07 .03 29-00 .76 12-28 .80 1-11 .18 LT “1-"? -017 07“ 12-28 071 .66 1-11 .63 .82 29-00 .63 .43 .60 12-28 031 035 .65 1-11 .26 .41 .60 LNFB “1-“? 096 .13 -001 096 29-140 .22 035 -013 -026 12-28 -.36 -.31 -.25 -.00 1-11 -.89 .06 -.50 -.37 1 Natural log transformation of PPFD 115 Figure 6. The relationship between solar time and photosyn- thesis (PgA), photosynthetically-active photon flux density (PPFDe), stomatal conductance (CON) and leaf temperature (LT) for Tristis and Eugenei leaves at various crown posit- ions measured during 17 July-1979. Stars (A) : immature leaf; circles (B) = recently-mature leaf; asterisks (C) = leaf in center of mature leaf zone; triangles (D) = lower- crown mature leaf. r Tfi f 11112141618 20 r ‘08 116 TR!ST!S 0m: G . 0 F 0 E 0 1.3.0 2 1% 2 1. 2 \\\\\ \ \ N I 8 |\\\\\\\\.. I8 \\ 05“ o 8) 001.111 . 11A 1. O.LWNTEKi 1. A. .1: .1 1n llrll / v 6 0!! r 6 I \o 6( l».-fll..v7|k ..1 ..MNIIILHJ. 1. V1 \8 1. E I: . also . 1 \ oo 7,...“ r A ..... .\ .. r 4 “\x. 4 M .19/ ..w 1 .valiswda 1 an} 1 n 0 . r 2 s \\\\ v 2 \\\ 2 41.1“nv1u‘6 1 . ubi‘gtlfiuuunfl .cl. fil-‘IQNI. cl. R / s . \ 6|“. /\ 0 s . r0 91‘ t 0 \V/ 0 0 m on” B. .l ..1 11:1lnuunu11J1\Jn .l Clan“ 1. O I . :...1.1~.m\- . .. . r S "H4 8 c’11.]..WII 1 . .. 8 A.MQ 8 1 a 1a $1 1‘ a 4 [ft 1 1 1J1 I 0.0 m; 0; 0.0 0.00 00-0 00m: 000 00 a; 0.0 .10 0.0a . .0 0 A 0 C I?“ 2 1110*2 2 .. . . .8 1.. 8 1...... .m 1 lurk Fm ..1, r I.\ . . a .s .m in :0... “MK ..1 d —t \\ t 1' I 4 T 4 k V 4 w H‘ 90“ 1 1 \ Ill 1 T l 1 9... v2 ‘I‘MI ‘ ‘ r2 I} 1w! 1 l o’clll‘ 1% , r 0 rnu .‘flo To . .0 .od- a 1.. 1 es” 1| 0 i1.) . . 8 15A: 08 S o 9 8 a o w JP!- ..1-La ‘6 0.10 0: 0H_ 0.0 0.00 00-.0 00? 000 NS 0.10 1.0 0.00 91m .55 200 9191:. 0.083 momma. ATmT-c N00 95 (an. 117 Figure 7. The relationship between solar time and photosyn- thesis (PgA), photosynthetically-active photon flux density (PPFDe), stomatal conductance (CON) and leaf temperature (LT) for Tristis and Eugenei leaves at various crown posit- ions measured during 15 August 1979. Stars (A) = immature leaf; circles (B) = recently-mature leaf; asterisks (C) = leaf in center of mature leaf zone; triangles (D) : lower- crown mature leaf. _118 TP18TIS _.. .0 2 18 16 1 14 1 12 1 10 1 18 00 1C 2 .8 1 16 1 r4 1 T2 1 To 1 18 W 4 J Nm «N 2 Q0 8.0 5 bu 10 12 14‘H318 20 Y T f r V Y W a O.N m. 8 0 000 ma0 0.q0 o.N m." o WI 000 0uq. ATm EEV zoo 00mm 0000 O 8' l5--l‘--'|l|' ‘58 ‘0‘- 8“ ‘0 I'll! I- 0 '0 000 q0 II II a. 5 8 0‘! W511! 0000 000i 000 q. 91.078 20:03 momma E 0 2 8) 1h 8( 1E 4M .1.1I1 2 11R 0mm 10 S 8 0.0 . e.0 0.qu A U 2 8. 1h. 6/ 1:: 4M 1T1“ 2 1R 10. .10 S R N; . 0.00 m E N00 95 <00 119 Figure 8. The relationship between solar time and photosyn- thesis (PgA), photosynthetically-active photon flux density (PPFDe), stomatal conductance (CON) and leaf temperature (LT) for Tristis and Eugenei leaves at various crown posit- ions measured during 29 August 1979. Stars (A) = immature leaf; circles (B) : recently-mature leaf; asterisks (C) : leaf in center of mature leaf zone; triangles (D7 = lower- crown mature leaf. _12o EUGENEI WIJ'JIJ'III mm mm em wfi vw mg 8; S m I l I I I 1012141818 20 fi fl j 1012141818 20 v v v 8 ‘% ‘% 8 j 101214181820 1 T 8 :.N m; o; ma 9% v v 10 12 14 16 18 20 I 8 1|4J||4||l 9N m; a; ma 0.00 ATm EEV Zoo F. .0 9. -8 .6 .4 -1.! ....... 8 ..fl. .. .- .0 .8 r oovw oowfi Dow Q0 Eu .0 7. .8 .6 T4 .2 .0 T oovW com“ com Q0 ATmTE 2083 woman. ABCD toma v 1012141818 28 SOLAR TIME (h) I V 8 F V 181214181826 SOLAR TIME (h) 8 N.~ m.o v.0 o.oo ATmTE «out mEV TH where: C = tan Nalt x D; D = the distance between trees; Nalt = the altitude of the leaf normal (Nalt = 900 - Nza; Appendix A); LDFB = the leaf's vertical distance from the base of the tree; and TH = tree height. Otherwise, the leaf received diffuse light from the surrounding vegetation. If the leaf was directed towards the open sky, it received the full diffuse light from the sky calculated in (6) (i.e., in this case, PPFD = PPFD ). This assumes dif,s dif an isotropic sky for diffuse light. If the leaf was direct- ed toward the surrounding vegetation, then PPFD was dif attenuated according to Beer's Law -kLAI PPFD = PPFD x e (9) dif,v dif ' where: PPFD = diffuse light received from the surround- dif v ing vegetation; k = extinction coefficient for diffuse light; and LAI = cummulative leaf area index above the leaf 154 -2 -2 (m m ). k was obtained from (Monteith, 1969) k = cos 5 cosec B (10) where: 5 = the mean angle between the leaf normals and the sun's rays (Appendix A) and B = the sun's altitude (Appen- dix B). Direct PPFD incident on a leaf (PPFD ) was found dir 1 from Lambert's cosine law (Robinson, 1966) ’ PPFD = PPFD x cos 6 ' ' (11) dir,l ps Soil reflection was calculated by attenuating PPFD as it passed through the vegetation to the soil surface,psand then by attenuating the reflected light as it passed up through the canopy to the vicinity of the leaf. The down- ward attenuation of light was calculated from ‘ -kLAI PPFD : sinB x PPFD x e x r (12) sd ps 3 where: PPFD = downward attenuation of PPFD ; LAI = cummu- sd ps lative LAI to the soil level; and r = the reflectivity of s the soil surface (r was 0.07 for the soil in this study). 3 Light available to the leaf (PPFDs ) was then calculated oil from -kLAI PPFD : PPFD x e (13) soil sd where: LAI = cummulative LAI from the soil to the leaf. When the adaxial leaf surface was directed toward the 155 sun PPFD = PPFD + PPFD (14) AD dir,l dif where: PPFD = adaxial PPFD and PPFD = PPFD or - AD dif dif,s PPFD . Abaxial light was then obtained from dif,v PPFD = (PPFD x cos p ) + (cos Nza x PPFD ) (15) AB dif,v soil 0 where: PPFD : abaxial PPFD and p = 90 - Nza. The AB assumption was made in (15) that abaxial diffuse light was received horizontally from the surrounding vegetation when the adaxial surface was directed toward the sun. When the abaxial leaf surface was directed toward the sun PPFD : PPFD (16) AD dif were: PPFD = PPFD or PPFD , and dif dif,s dif,v PPFD = (PPFD x cos v ) + PPFD (17) AB dir,l dif + (cos Nza x PPFD ) soil where: u = the angle between the normal to the abaxial leaf surface and the sun's rays. MW Trees with similar numbers of leaves were measured on 156 8-20-79 and 7-22-80 (one tree per clone per date); these trees were the basis for clonal comparisons. Although the sampled trees had similar leaf numbers, they were at differ- ent phenological stages in both years, i.e., Eugenei was actively producing new leaves at its apex whereas budset had occurred in Tristis. The influence of leaf orientation and leaf size on within-tree light interception was assessed by comparing measured light interception values against estimates of PPFD for unobstructed leaves. The light interception model was used to estimate PPFD for leaves within the crown which were shaded. In this manner, an estimate of light interception for an unshaded leaf complement was obtained. The light interception model was also used to estimate PPFD for leaves mathmatically rotated so that their laminae were perpendicular to the sun (i.e., N was parallel to V ). The influence of leaf oriegtation and leaf :ize on single-leaf and whole-tree photosynthesis (PgL, ug C0 3-1 leaf.1 and PgT, ug CO 3.1 tree-1, respectively) was assess- ed by substituting meisured and estimated PPF values into light response curves (i.e., PPFD versus PgAeEmg 00 m- s- 1)) developed earlier for these clones (Chapter III; Fig. 2). To discern how differences in leaf area, leaf orient- ation, and photosynthetic response to light influenced clonal PgT differences, PgT was recalculated for Tristis using: (1) Eugenei's leaf area and PPFD/PgA curves (to 157 Figure 2. The relationship between photosynthesis (PgA) and PPFD for field-grown Tristis and Eugenei leaves during their first growing season. A = upper-crown leaf (LPI 3); B = recently-mature leaf (LPI 9); C = mature leaf midway between B and D; and D = sixth mature leaf from the base of the stem. These curves were generated from data presented in Chapter III. PgA (mg CO2 m‘28’1) c9.0 0.4 PgA (mg CO2 00-28”) c9.0 0.4 1.2 0.8 1.2 0'8 158 TRISTIS _______ B d ,/ ”””” 44- \8 .1 _________________ D ' 800 1800 2400 EUGENEI rC l -----_----—--—-- ‘9‘- ‘ ’ PPFD (,umole m'zs"') 800 1800 2400 159 examine the separate effect of leaf orientation), (2) Eugenei's leaf orientation and leaf area (to examine the separate effect of the PPFD/PgA curves) and, (3) Eugenei's leaf orientation and PPFD/PgA curves (to examine the sep- arate effect of leaf area). For example, to isolate the seperate effect of leaf orientation, PPFD rates measured in Tristis for each leaf were substituted into PPFD/PgA curves developed for Eugenei and the resultant PgA rates were extrapolated over Eugenei's leaf area. RESULTS The two poplar clones had widely contrasting leaf dis- plays: leaves were oriented vertically (i.e., erectophile) in Eugenei and horizontally (i.e., planophile) in Tristis (Fig. 3). Leaf direction was largely controlled by phyllo- taxy in both clones; however, slight deviation from a strictly phyllotactic series occurred due to twisting and bending along the petioles of a few leaves. Midrib angles gradually increased basipetally in both clones causing leaves to be nearly upright near the apex, more horizontal in the middle-crown region, and sloped slightly downward in the lower crown. Leaves exhibited greater variation from the horizontal (i.e., leaf axis #1 was horizontal when the midrib angle equaled 90°) in Eugenei than in Tristis. Lamina angles differed dramatically between clones. Lamina angles varied only slightly from the horizontal (i.e., leaf 0 axis #2 was horizontal when the lamina angle equaled 9O ) in 160 Figure 3. Leaf azimuth, midrib angle, and lamina angle by LPI for the entire leaf complement of single Tristis and Eugenei trees measured on July 22, 1980. 161 n 1 40 :0 M 40 6 0 6 II II II 3 3 LPI EUGENE! 20 20 1. u u .. .0 r I I 0 u I ull1u11: .l m In (1].. 1.1 011ml. Q1 owe. EN 2: om an 2.: m? om me no 2.: m? om we on 1O 1 10 m DINING 1110111111410 m r m— 0 10 ..U m 1110111111110 3 3 3 m 1411111. S m 1110.111111Im ran/u. finU rm 11m 2 U m 1011.411 . HUN-Ila ml1m1111|¢1111 mrU .0 r0 U 11. .1.. 1|. ml111111101||111 114.41%; 9% EN 2: om go 2.: m? mm- 9. on 2.: m? mm We go Homow IHDXHNG Ipmoz Howey mqozc mmmowz Home“ mqozc ¢ZHZ¢4 LPI 162 . ' 0 Tristis; in contrast, lamina angles varied up to 90 from the horizontal in Eugenei. Eugenei's more vertical (leaf display was derived largely through rotation around leaf axis #1, i.e., by adjustment of the lamina angle. The. azimuth and zenith angles of N are plotted in Figure 4 for all leaves of one tree perLclone measured on July 22, 1980. Figure 4 is a two-dimensional representation of three-dimensional N projections onto the celestial sphere and illustratesLto which region of the celestial. sphere each leaf was directed. Tristis leaves were directed near the zenith and had N zenith angles less than 45°. The two exceptions to this :ccured at leaf plastochron index (LPI, Larson and Isebrands, 1971) O and 3 which were vertical leaves near the apex with N zenith angles of 50 and 650. In contrast, N zenith angles in Eugenei ranged from O0 to 80°. Leaves dig not appear to have an azimuthal preference in either clone. Diurnal leaf area projected onto a plane perpendicular to V differed greatly between clones (Fig. 5). Tristis had a bill-shaped pattern with a peak occurring at solar noon. The adaxial surface comprised most of the projected leaf area in Tristis, although a small proportion represented the abaxial leaf surface directed toward the sun during early morning and late afternoon. The PROJLA/LA ratio varied from 0.26 to 0.84 for Tristis leaves (Fig.6). Total projected leaf area also peaked near solar noon in Eugenei, but 163 Figure 4. Equal-area projection of the azimuth and zenith angles of N for Tristis and Eugenei leaves measured on . L August 20, 1979. Latitude lines denote zenith angle and longitude lines denote north azimuth angle. no no 300 N W. zoo zoo no no 3' zoo C :uo . no 300 NW C no . zoo . 240 no 3* zoo 164 50 70 90 I40 I20 100 flflSflS 40 EUGENE! IO 60 40 0 20 B 165 Figure 5. Diurnal leaf area projections onto a plane perpendicular to the sun's rays for Tristis and Eugenei leaves measured on August 20, 1979. .166 83! TOTAL [I] ADAXIAL A ABAXIAL TREWES cows omms owe omm- p-28 SSE /, l 18 16 14 12 10 OD EUGENEI 12 14 10 SOLRR TIME cows omms now. own 9.28 58% (H) 167 Figure 6. Ratio of total leaf area/total projected leaf area (PROJLA/LA) for Tristis and Eugenei leaves for the diurnal period of August 20, 1979. PROJLR/LR 168 EUGENE! TREWES F l— 1 ‘8 81812141818 20 SOLRR TIME (H) 169 Eugenei projected less leaf area toward the sun than Tristis during the noon period (Fig. 5). Eugenei projected substiantially more leaf area toward the sun than Tristis during early morning and late afternoon, and abaxial projections comprised a greater proportion of its total projected leaf area than observed for Tristis. The PROJLA/LA ratio in Eugenei was lower and less variable than in Tristis, ranging between 0.54 to 0.66 (Fig.6). Although Eugenei had 10% more actual leaf area than Tristis on August 20, 1979 (LA = 1691 and 1527 cm.2 for Eugenei and Tristis, respectively), Eugenei had only 3% more leaf area projected toward the sun over the diurnal period. The separate effects of leaf orientation and mutual shading were assessed by comparing the light interception of leaves measured under natural conditions against estimates of light interception for a totally unshaded leaf comple- ment, using the light interception model to estimate PPFD AD and PPFD in full sun for all leaves that were shaded. A AB good correlation between known and estimated PPFD and 2 AD PPFD (r = 0.7) was obtained for unobstructed leaves using AB the light interception model. The difference between estimated PPF on PgT for an unshaded' versus a shaded leaf complement trepresented the effect of within-tree mutual shading. Mutual shading resulted in a 14 1 reduction in PPFt and a corresponding 6 1 reduction in PgT in Tristis on July 22, 1980 (solar time (ST) = 10.00 to 14.00 h) (Table 1). PPFt was reduced in 170 cor hmm can on Lmasofiucoogom .ooumsncs no, mpm uoomnnc: Pop . :om cogsnmox Huqummw me me: can op smasofiocoocom .uoomnnca cpm Nam ooomnmcs :om emm accommoz HHMHHHH A ooeo n moo was A ooeo n oHos av aaaaaaaauwmaqqu P mum P mama .csm on» on Lmasouocoacoq coucoago no>moa cam mo>moa ooumsmcs zaamuou Lou nonmawuno on cocmaaoo omm— .NN hasw :o Aoswu sodomy : oo.=- ncm oo.op coozuon cocsnoos no>moa Hocomsm com nwunwgh too “easy nanoeoeznooona one Aoeaav aofiooooeooafi nemaa ooeoaaooos .. manna 171 Eugenei by 3 1 , which corresponded to a 4 1 PgT reduction. The separate influence of leaf orientation was assessed by comparing the unshaded leaf complement in its natural orientation against estimates of PPF for a complement of unshaded leaves oriented perpendiculartto the sun. PPF for unshaded Tristis leaves in their natural orientation wa: 191 less than PPF for unshaded leaves facing the sun (Table 1). This reductio: corresponded to a 2 1 reduction in PgT. PPF for naturally oriented unshaded Eugenei leaves was 42 1 les: than for leaves facing the sun, resulting in a 15 1 PgT reduction (Table 1). PgT was 21 1 greater in Tristis than Eugenei during midday on July 22, 1980 (Table 1). When both clones were given a common leaf area and PPFD/PgA curves, PgT was great- est in Tristis by 15 1 (Table 2); when both clones had the same leaf orientation (and therefore, the same within-tree PPFt) and leaf area, PgT was greatest in Tristis by 23 1; and when both clones were given the same leaf orientation and PPFD/PgA curves, Eugenei exceeded Tristis' PgT by 17 1. DISCUSSION This examination of photosynthesis within one-year-old poplar trees revealed that leaf orientation and leaf size were important determinates of light interception and photo- synthesis at the level of the single leaf as well as the whole tree. Even in the first growing season, significant within-tree mutual shading occured and light was attenuated due to the direct effect of leaf orientation. 172 :om cogsmmos I mHHmHmH «a “sane amp noseso «ma\amaa a as n.aoeomsm \3 neonate «m2\aeas Ammo cam <4 a co n.8oeomsm \3 magnate ca Amps cos noseoo «m2\aaaa e «a n.0oeomsm \3 naanaea Pop ooeonooa . Hmzmosm A coca n moo may amemH mqaudu P mum aqaaaazquwmzqqm .oumc accommos m.aocom:m scum monocommHo acoocon oumoficcfi nanosucogma :H mcooanz .ommp .mm >st .Aosfiu Lmaonv s oo.ap on oo.cp cocsmoo: .mocoao coozuon acouncoo vac: oLoz Amouoso so .~<4V mono mama .Aoqv coauwucoHLo.umoH con: Hum mo nonmafiumo on cocmasoo “away nanosuzznouona oogpaamaou cogsnmos a.Ho=omsm can nfiunfigh .N manna 173 In the first growing season, single-stemmed trees were examined whose crowns were essentially isolated from their neighbors. This may, at first, appear to be a simplistic approach; however, as Thornley (1976) emphasized, the iso- lated plant is generally a more difficult theoretical prob- lem than the crop growing as a stand. In addition, it is essential to identify the geometrical and biological parameters which control light interception and photosynthe- sis within a realtively simple crown before advancing to older, more complex trees and whole stands. A leaf area projection pattern which promotes photosyn- thesis during early morning and late afternoon may be mOre conducive to Eugenei's growth than one which maximizes leaf exposure during noon, since Eugenei had a high shoot/root ratio which predisposed it to water stress during the hot noon period. The low shoot/root ratio in Tristis may have allowed 'its horizontal leaves to take advantage of the favorable light environment occuring during solar noon with- out suffering 8from stresses associated with high leaf temperatures. The influence of leaf orientation on light interception can be examined on at least two levels: (1) direct effects - the influence of leaf orientation on individual-leaf light interception, and (2) indirect effects - the influence of leaf orientation on mutual shading within the tree. Tristis' leaf display produced greater light losses from mutual shading but less reductions due to leaf orientation 174 than Eugenei's leaf display. In effect, the Tristis leaf display is a compromise, with irradiation of its lower crown sacrificed so that upper-crown leaves are fully irradiated. In contrast, full irradiation of the upper-crown leaves in Eugenei was compromised so that leaves could be irradiated throughout its crown. Since upper-crown Eugenei leaves fail to intercept much of the available light, very little mutual shading occurred. Reductions in PPF resulting from the combined effects of mutual shading and lzaf orientation were remarkably simi- lar in the two clones. However, the crown regions in which these reductions occurred differed markedly: lower Tristis leaves and upper- and middle-crown Eugenei leaves experienc- ed reduced PPFD rates. Leaves in different crown regions respond differently and in a non-linear fashion to intercepted light. Therefore, the impact of these light interception patterns can only be assessed by considering the photosynthetic response of leaves in specific crown regions to intercepted light. The PgT reduction per unit PPFt reduction was proportionately less in Tristis than Eugenei because Tristis PPFD reductions occurred in its less productive, lower-crown leaves, whereas the majority of Eugenei's PPF reductions occurred in its productive upper- and middle-grown leaves. Several investigators have suggested that photosynthetic production would be maximized in a crown which disperses light so that a large number of leaves throughout the crown are irradiated below light sat- 175 uration (e.g., deWit, 1965). However, leaves in the lower- crown region must be photosynthetically responsive to light received for this type of dispersal pattern to be effective. Although an even distribution of light occurred in Eugenei, its lower-crown leaves did not photosynthetically respond to this favorable light environment to the extent that losses incurred in upper-crown leaves were offset. In fact, Eugenei lost 10 1 of its leaf complement during midseason as a result of senescence in the lower-crown (Chapter II), negating any beneficial effect of its light dispersal pattern. It would be difficult to experimentally isolate the separate effects of leaf orientation, leaf area, and inter- cepted light without mechanically or genetically manipulat- ing the two clones to vary one factor while holding the others constant. Although these factors can probably be manipulated genetically over a wide range, genetic manipu- lation could be hampered by pleiotropy. Mechanical manipu- lation of leaf orientation or leaf area may induce unwanted plant responses which would confound the comparison. As an alternative, an estimate of the separate effects of these variables was obtained by mathmatically varying one factor while holding the others constant. To predict adaxial and abaxial PPFD, the direct and diffuse light received by each leaf must be estimated. Estimating the diffuse light component has traditionally been the most diffucult task confronting modelers, since 176 light emitted from each region of the sky varies with atmospheric conditions, solar azimuth, and solar altitude. In addition, diffuse light impinging upon a leaf is dependent upon the orientation and position of the leaf within the tree and degree of shade. Prediction of the diffuse light contribution of each sky region under a wide range of plant and atmospheric conditions would be diffi- cult, if not impossible. Therefore, a more generalized approach to estimating diffuse light was employed in the model presented here. The model supplied adequate predict- ions of adaxial and abaxial direct and diffuse light for unobstructed flogging leaves within one-year-old trees; how- ever, patterns of intra- and inter-tree shading were not considered. A much more'sophisticated model than the one presented here would be required to predict shading patterns within individual trees; such a model would facilitate the development of ideotypes for flogging trees. The PPFD/PgA response of leaves was found to be the most important factor contributing to the observed PgT difference, followed closely by leaf area and leaf orient- ation. Clonal differences in the PPFD/PgA curves may be due to several factors: (1) different leaf anatomy (e.g., different mesophyll thickness per unit leaf area, different chlorophyll concentrations), (2) different residual resist- ance to CO movement into the leaf (Nelson and Ehlers, 1983), or %3) different leaf aging patterns. The initial slopes of the PPFD/PgA curves may profoundly affect PgT 177 since many leaves were oriented so they received less than saturating PPFD in the linear region of the curve. There is an indication that leaf orientation was as important as leaf area in accounting for the observed PgT difference. Tristis compensated for its smaller leaf area by arranging its leaves to maximize light interception with- in the productive region of its crown. Although total leaf area per se is known to be an important determinate of growth in poplar trees (Larson and Isebrands, 1972), the orientation of leaves within a tree's canopy is an important factor which cannot be ignored. It would appear from our results that the horizontal leaf display of Tristis was best adapted to the relatively open growing conditions present during the first growing season. This conclusion supports results obtained from computer simulations for several other crops (deWit, 1965; Duncan et al., 1967; Ross, 1970; Oker-Blom and Kellomaki, 1982). However, extreme caution must be used in attempting to determine which strategy was "best" between the two clones. This discussion has centered on the solar noon period, which may have produced a bias toward Tristis. The entire diurnal period must be considered before a "best" strategy could be identified. Even then, ideal crown struc- ture depends upon several dynamic, intercorrelated factors. The influence of leaf display, crown structure, leaf area development, and environment on photosynthesis must be exam- ined together on a diurnal and seasonal basis before an 178 optimum crown structure can be identified. 179 APPENDIX A. CALCULATION OF LEAF AND SUN VECTORS- Consider a X-Y-Z coordinate system where the positive X axis is directed south, the positive Y axis is directed east, and the positive Z axis is perpendicular to x and Y and directed upward. To quantify a leaf's three-dimensional orientation, the angles between these major axes and two principal vectors which describe a leaf (Fig.2) must be determined. The leaf vectors are: (1) V , which extends along the midrib from the leaf's base to tip (leaf axis #1), and (2) V , which is perpendicular to V in the lamellar plane andzoccurs at the point of greatesl leaf width (leaf axis #2) (Max, 1975). Typically, V1 and V' can be described using direction 2 cosines (Flanders and Price, 1973) V = cos c (i) + cos B (J) 1 + cos Y (k) (1) V = cos a (i) + cos B (j) 2 + cos Y (k) (2) where: a. : angle from the X axis; 3 = angle from the Y axis; and 7': angle from the Z axis. V and V can also be 1 2 described using angles which are more readily measured in the field V = sine sin‘b (i) + cose sinw (j) + cosw (k) (3) 1 180 V .-. -cose sinn (i) + sine sinn (j) + cos 0 (k) (4) 2 where: 1p: midrib angle, the vertical angle of leaf axis #1; 0 lamina angle, the vertical angle of leaf axis #2; and O the east azimuth of leaf axis #1 (Max, 1975). These formulae differ from those derived by Max (1975) since a different X-Y-Z coordinate system was used. The vector normal (i.e., perpendicular) to V and V 1 2 (N ) can be found from: N = V X V , the vector product of L L 1 2 V and V (Thomas, 1969; Max, 1975). More specifically 1 2 N = {cose sinw cosn - sine cosw sinfl } (i) (5) L + {-cos@ cosw sinn - sine sinw cosfl } (j). 2 2 + {(sine ) sinw sinn + (cosG ) sinw sin0}(k) N must be normalized to unit length by L N = (i/INE) + (j/IN1) + (k/IN!) (6) L where: i, j, and k denote the i, j, k components of NL‘ defined in (5) and 2 2 2 0.5 IN! = (i + j + k ) (7) To. find‘ the north azimuth of N (Nazm), the angle L between the projection of N onto the X-Y plane and any L major X or Y coordinate axis must be determined -1 O = tan Ii/j! (8) where: 11 denotes the absolute value. Then, if i>0 and j>0, 181 o o Nazm = 90 + o ; if i>O and j<0, Nazm = 270 - o ; if i>0 o o and j<0, Nazm = 90 -|o ; and, if i<0 and j<0, Nazm = 270 + To find the zenith angle of N (Nza) L o Nza = 90 - T (9) where -1 T = tan lk/ci (10) and 2 2 0.5 ' c = (i + j ) (11) Calculation of a vector describing the sun's rays (V ) s proceeds as described for V 1 V = sincn sin C (i) + cos 0 sin C (j) + cos c (k) (12) s where: w = the sun's east azimuth and c,= the sun's zenith angle. 0 and C can be found using the method described in Appendix B. V must then be normalized to unit length using the the approazh described in (6) and (7). The angle between N and V ( <1 ) can be obtained from L s the inverse cosine of the dot product of N and V (Flanders L s and Price, 1973; Max, 1975) -1 o = cos {(N * V ) / (!N 1 x IV 1)} ' (13) L s L s where N * V = (N (i) x V (i)) (14) L s L s 182 + (N (j) x V (j)) L s + (N (k) x V (k)) L s and IN I and IV I are found as in (7). L s 183 APPENDIX B. CALCULATION OF SOLAR ALTITUDE, AZIMUTH, ZENITH ANGLE, AND HOUR ANGLE Solar declination can be obtained using (deWit, 1978) 6 = ( “/180) x -23.u x cos {2 x n x (DAY + 10)/365} (1) where: 5 = solar declination (radians) and DAY = Julian date (i.e., the number of days since January 0). Solar altitude can then be obtained from -1 3 = sin {sin 5 sin A + (2) cos 6 cos A cos{21 (t + 12)/2u}} where: g = solar altitude (radians); A = latitude (rad- ians); and t = solar time (h). Solar azimuth can then be calculated from (Smart, 1962) -1 w = cos {sin 6 - sinB sin A )/ cos 8 cos A )} (3) Equation (3) gives the eastwardly azimuth from north when t 12.00 h and the westwardly azimuth from north when t 12.00 h. The sun's zenith angle ( C ,radians) can be calculated from The hour angle ( n) of the sun can be calculated from (Duffett-Smith, 1981) -1 n = cos { (sin 8 - sin A sin 6 )/(cos A cos 6 )} (5) 18“ REFERENCES Biggs, W.W. and Hansen, N.C., 1979. Radiation measurement. Li-Cor Inc., Lincon, Neb. 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